
Why a Dutch court stopped high school students from exchanging schools - adamnemecek
https://medium.com/popular-choice/why-a-dutch-court-stopped-high-school-students-from-exchanging-schools-1315303a48b6
======
jpfed
>By trading places, students could get another shot at a place. At schools for
which they already had a go in the lottery. This would give them better
chances. At the expense of students that don’t (or can’t) trade. This is
unfair.

This is culturally alien to me; the students receiving the benefit are not
harming other students.

>Another argument, that is related, is about strategizing. Students were told
(correctly) that their best strategy was to give their true preferences. If
trading were allowed, this would not be true. It would pay off for students to
put popular schools high on their list. A spot at these schools would be good
trading material.

Solution: only allow trades that are in accord with the students' submitted
preferences. That is, if Alice prefers Central to Devonshire, and Bob prefers
Devonshire to Central, then we could allow Alice and Bob to switch _if_ their
submitted rankings indicated that these moves were consistent with their
desires. There would be no incentive to lie.

~~~
Sniffnoy
> This is culturally alien to me; the students receiving the benefit are not
> harming other students.

It's not just "culturally alien"; it's a straight-up error.

> Solution: only allow trades that are in accord with the students' submitted
> preferences. That is, if Alice prefers Central to Devonshire, and Bob
> prefers Devonshire to Central, then we could allow Alice and Bob to switch
> if their submitted rankings indicated that these moves were consistent with
> their desires. There would be no incentive to lie.

It's not obvious to me that this is true? Relevant discussion over on /r/math:
[https://www.reddit.com/r/math/comments/6uyfle/why_a_dutch_co...](https://www.reddit.com/r/math/comments/6uyfle/why_a_dutch_court_stopped_high_school_students/dlwtroo/)

~~~
cortesoft
Wait, why is that a 'straight-up error'? They explained why it would harm
other students - because it would incentivize students to choose popular
schools instead of schools they actually wanted, in hopes of gaining a good
trade opportunity. They don't want strategy to come into play, because some
people are better at strategy than others.

It isn't an 'error', it is just a decision that they don't want strategy to be
a factor.

~~~
Sniffnoy
Yes, the incentives this sets up could be bad for subsequent rounds; that is
absolutely a real problem. But this passage seemed to be suggesting that
trading, in and of itself, harmed students who were not involved in the trade,
and that's not correct.

~~~
cortesoft
Something being unfair is not the same as something harming someone else. Lets
say I have a cookie, and there are 10 kids in front of me who like cookies. If
I give any kid a cookie for any reason, it doesn't HARM the kids who don't get
a cookie; they are no better or worse off than if the cookie never existed.
However, suppose I decide to give the cookie to the tallest kid - even though
none of the other kids are harmed, this is still not a 'fair' situation.

You can do no harm and still be unfair. Whether that is bad or not is
subjective, but it is still unfair (in the sense that every kid has an equal
chance at the cookie).

~~~
Sniffnoy
Sorry, I just realized that I failed to point out which part I was saying was
"a straight-up error"; it's kind of buried in the sentence. My mistake! With
emphasis this time:

>By trading places, students could get another shot at a place. At schools for
which they already had a go in the lottery. This would give them better
chances. _At the expense of students that don’t (or can’t) trade._ This is
unfair.

The emphasized part is what I'm objecting to. Sorry about that.

~~~
Retric
Let's say there is a lotto for concert tickets. If I pay 1,000 people to take
part in that lotto who don't want the tickets then I get an 'unfair'
advantage.

The logic is similar for the school lotto as people would target schools based
on their ability to trade not necessarily their actual preference. This would
lower the odds of people who otherwise had fewer options.

AKA, if only bob or sam want a spot sam's odds are 50/50%. But, of ted joins
but would always give his spot to bob then sam's odds are 1/3 and bob's odds
are 2/3.

------
air7
Win-win swaps could be done automatically by the lottery system. This
eliminates the non-fairness objection (as this optional upgrade can happen to
anyone). It does theoretically create room for strategizing though: If there
is a very popular school that I don't want to go to, it makes sense to put in
down as option #3 or #4 because if I get it, I might slingshot back into my
#1-#3 options.

~~~
vanderZwan
> _It does theoretically create room for strategizing though_

And that is the exact issue with it: it would soon be common knowledge that
you should do so, and then the people who don't consciously try to game the
system would be at a disadvantage.

In general that seems to be the goal: devising a system that cannot be gamed
in any other way than giving your honest preference. In other words, ensure
that the system is a self-enforcing protocol.

[https://www.schneier.com/blog/archives/2009/08/self-
enforcin...](https://www.schneier.com/blog/archives/2009/08/self-
enforcing.html)

------
abalone
San Francisco United School District uses the multi-DA system, but here's the
kicker: it _bakes exchanging into the algorithm_.[1] They call it "trading
up"; most parents here refer to it as "swapping".

It works more or less as described, where you list off all the schools you
want in order of preference. It runs lotteries for each of them in parallel
and you get the highest listed one you win. But then it does one more thing:
If it finds mutually advantageous swaps, it does so automatically and
instantly. In other words, it's not up to or necessary for the student to do
it manually.

In fact this feature is detailed by the Ivy League team that put it together,
including Alvin Roth, as early as 2010.[2] So while this article is well
written it seems to give a less than complete picture. Why did Amsterdam not
adopt this feature?

P.S. There is _much to be said_ about the SF lottery system which is a fun /
highly stressful topic for nerds and parents. If you like these kinds of
problems I encourage you to take a look. It also tries to solve for giving
preferences to neighborhood schools and disadvantaged families, while also
offering special language and K-8 programs that serve the whole city fairly.
The goal is to eliminate strategizing as much as possible, but it's very
interesting to see people figure out some hacks.

[1] [http://www.sfusd.edu/en/assets/sfusd-
staff/enroll/files/2012...](http://www.sfusd.edu/en/assets/sfusd-
staff/enroll/files/2012-13/Assignment-Transfer%20process%20explained.pdf)

[2]
[http://web.stanford.edu/~niederle/SFUSDBoardPresentationFeb....](http://web.stanford.edu/~niederle/SFUSDBoardPresentationFeb.17.2010.pdf)

~~~
bigethan
I disagree about the "fun" part having just gone through this with my first
kid. I agree with the Dutch, swapping (at any point in time) adds an edge of
unfairness to the process:

\- In a situation where all decent schools are oversubscribed swapping 100%
encourages (and rewards) setting up your school list strategically. Which
helps out families that have the time to collect the information needed and
sort their schools appropriately (we spent a bunch of time researching /
planning here, but knew off other families who _really_ got into gaming the
system)

\- In one of the meetings where the slide you linked in [1] was displayed,
they offhand mentioned that the swapping order is done alphabetically. When
asked if kids with A* names will get better swaps they kinda ignored the
question and moved on. But how are multiple tied swaps resolved?

\- Also, from what we were told, the swapping doesn't respect the "lottery
weight" that locals, poor test score neighborhood kids, or siblings get. If
that's important, shouldn't it apply to all phases of the process? (I'm aware
the math here might get out of hand)

I started out thinking that the swapping was a good idea, but when I saw how
much it encouraged and rewarded strategy in building the list of schools I
changed my mind. It's not a fair process. It's a system that rewards families
that have likely already been rewarded by society.

~~~
dllthomas
> If that's important, shouldn't it apply to all phases of the process?

Doesn't that same reasoning apply to increasing the weight? Maybe it's so
important and not more important.

------
gnicholas
> _To allow trading would be to enable strategic behavior in future years...it
> could also give an unfair advantage to students that are better at
> strategizing — and to students that have more resources to make good
> strategic decisions._

Similarly, it could enable wealthy students to buy slots from poorer kids.
Poorer kids could choose to prioritize schools that are popular, but that they
don't actually want to go to, in the hopes of trading places with a rich kid
who was willing to pay for the privilege.

------
skrebbel
Amsterdam is a very special place. You know how on HN everybody always
complains about insane all kinds of legislation in SF? Well in that respect,
Amsterdam is the SF of the Netherlands. So please let this taint your opinion
of Amsterdam, and not of Europe or the Netherlands.

They _really_ like rules and regulations there. More is better. Notably, the
whole concept of a high school lottery is culturally alien to most of the
country. Let alone a lottery with a 1000-page rule book and court cases.

~~~
paulannesley
> let this taint your opinion of Amsterdam

Why taint? The judge gave good reasons for disallowing trading. In particular;
if students know they can trade places later, they'll pile onto the most
popular schools (rather than their true preference) knowing that if successful
they can easily trade their place for another one (including their preferred
school which may not have selected them). Add to this the possibility of paid
trades, I think it's great they're keeping it fair and simple.

------
politician
If they allowed trading, then there's nothing to stop the lucky winners of
spots at popular schools from selling their spots, or for losers of spots to
offer bounties for their top choice. As an argument for, "Win-win swaps" comes
up a little thin when you consider the sort of economic shenanigans that folks
can engage in.

~~~
jseliger
_If they allowed trading, then there 's nothing to stop the lucky winners of
spots at popular schools from selling their spots, or for losers of spots to
offer bounties for their top choice_

Who cares? If people prefer cash to a spot at a particular school, let them
have it.

~~~
ricardobeat
We care, and you should care too: the effect of that policy would be the exact
opposite of fairness, the rich would go to the best schools while the poor
would get a handful of cash and the worst education.

~~~
chii
Also the cash goes to the parent, but the kids gets the shit school.

------
sannee
It would also be interesting to hear about why there are no entrance exams in
the dutch system (or at least the article does not mention them).

~~~
Rainymood
There are nation wide tests at the end of primary school (to get into high
school) i.e. CITO and NIO I believe. If you score well on these tests you get
a good 'advice' which is non-binding which this post is about.

I had a near perfect CITO score but a literally retarded NIO score because
they explained me how the test worked wrong (I was probably being stupid and
WAY took their words LITERALLY [1]). So they basically averaged my scores
(best and worst) and said "Well you go to the HAVO" which is average.

My parents did NOT sit well with that and just said "No he's going to
Gymniasum (highest possible class with Latin/Greek) whether you want it or
not. We all know he just screwed up there on that one tests because you
explained him the instructions wrong."

Anyway, 11 years later and I'm doing a PhD in applied mathematics. I'm really
happy my parents fought for me to go to Gymnasium and I'm so glad the advice
isn't binding. I'm not sure whether it still isn't binding or they changed it
somehow.

[1] The instructor told us that "at the end of your test you will have time to
finish your questions". So what stupid little me did was I made half the test,
then I waited till the time ran out and when they took my paper I asked "can I
finish the questions now?" And they just took my paper away.

------
neilwilson
You can always rely upon economists to exclude any human considerations from
the process.

There is no choice here because it fails the 80/20 rule of any hiring system.
Any less than 20% capacity spare and there is no free choice.

So since there is no actual choice, why give people one? Is it the same as
with toddlers - You can have red juice or blue juice - a way of giving the
feeling of control without actually having any.

Giving people a choice and then not giving them what they want causes loss
aversion responses. That is worse than not having any choice at all.

Kids want to go to the nearest school and the schools should be sufficiently
equipped to cater for all needs in the area.

Every other solution I've seen is more difficult than that one and is based
around psychological manipulation rather than solving the problem.

And no the 'free market' won't provide. You're supply side limited by the
number of people capable and willing to be teachers. That's why you have to
have a mass production system for education.

~~~
icebraining
Why can't capacity expand to adjust for demand? Sure, not always possible, but
in many cases it could be.

 _Kids want to go to the nearest school and the schools should be sufficiently
equipped to cater for all needs in the area._

Nearest school to what? I used to go to a school quite far from my home, but
within walking distance from my grandparents home, who took care of me for a
couple of hours after school. I had friends who went there because it was
close to the swimming pool where they trained.

We had that option because it was a non-profit school ran by a socialist
cooperative, instead of the local rigid public system (talk about ignoring
human considerations!).

~~~
neilwilson
Because there aren't enough teachers. Just like there aren't enough medical
staff. It just doesn't happen.

~~~
icebraining
You don't need more teachers, since the total demand (total number of
children) remains the same. You just need to move them around.

------
cm2187
French universities have adopted a similar system. For some reason they do not
like to select students based on merit, and there are more candidates than
seats, so they introduced a lottery to determine who gets to go to university.
It's very curious from the outside and even being French I can't think of a
good reason for this system. Basically telling students it doesn't matter how
hard you work in high school, it has no impact on whether you will work in a
bank or a factory...

~~~
sannee
Are French high schools reasonably homogeneous in their quality? Otherwise a
merit-based system would be massively discriminating against students which
made a poor choice (or live in an area without much of a choice).

~~~
cm2187
Not really. State controlled schools in theory are supposed to take students
based on postcode only, but in practice the most prestigious do their own
selection. And you also have lots of private schools that are even more
heterogeneous.

The French system is very paradoxical. By trying to be very egalitarian it is
achieving the opposite result.

For high schools, the postcode allocation makes that wealthy areas where
parent tend to be all highly educated have much better schools, whereas the
poorest suburbs where immigrants live when they first arrive in France, have
become educational toxic waste lands. And since teachers do not want to live
there or face these students, they also get bottom of the basket teachers and
high turnover.

The mainstream universities, because of a long standing practice of having no
selection, are chronically over-crowded and under-funded and their reputation
has gone down the drain, outside of a few disciplines, like medicine, where
incompetence has too great consequences, and which maintained a good
reputation based on competitive exam selections.

In parallel to universities, you have _grandes ecoles_ which are small
universities (student count wise) but very selective and very prestigious, and
from where the vast majority of company executives come from. In theory these
grandes ecoles are very egalitarian too, the entrance is based on a very
selective competitive exam in math, physics, economy, etc and are either free
or cheap (outside of business schools). To prepare for this exam, students go
through a 2/3 years preparatory school, with a very intensive and demanding
curriculum. Most students keep a horrible memory of these years and these
preparatory schools are known for being a "not for every student" experience.
As a result, teachers in poorer areas (who did not go through these schools
themselves) discourage good students from enrolling ("it's not for you, too
hard"), whereas parents who themselves went through this system apply pressure
on their kids to do it anyway. As a result, you end up with a massive
endogamy.

------
speleding
I'm the parent of a kid who took part in the 2015 school lottery in Amsterdam,
and since I had skin in the game I went as far as studying the original nobel
prize winning papers on the DA algorithms to understand exactly what was
going. This article is actually a really good summary, the amount of
misinformation out there being spread by journalists who did not fully grok
the (admittedly complex) system is astonishing.

One thing that the article only touches on is the "preferred placement" that
some schools managed to bring in from the old system, e.g. Montessori kids get
preference for Montessori schools. This ruins the elegance and inherent
fairness of the algorithm. In particular it makes it possible to do some form
of strategic selection again if you have a preferred placement option that you
can trade. This tends to benefit kids with clever parents disproportionately,
as the article notes.

A "lesson learned" for policy makers should be that even though an algorithm
performs better on being "fair" (Multi-DA), it can still be better to choose
an algorithm that is easier to explain. (They did end up switching to a
different algorithm the next year)

------
valuearb
Reason number ### for why lack of choice in education is bad

~~~
ucaetano
Yeah, the Dutch educational system is clearly failing, being the 9th best in
the world...

~~~
maehwasu
To what degree do those rankings simply correspond to average population IQ?
Genuinely curious.

~~~
ucaetano
Are you claiming that dutch people have genetic traces that lead to higher IQ?

Because a better education leads to higher IQ; so, if the Dutch people have
higher IQs on average, it might be because of the better education.

------
alkonaut
I thought the argument was going to be that exchanges would lead to poor
students applying for top schools only to "sell" their spot to the highest
bidder in a swap.

It would seem though that some exchanges could take place within the lottery
system itself. If two students were accepted to their second choices, and
swapping them would give both their first choices, then that should be an
optimization pass run after the lottery pass is done.

~~~
maxerickson
The single-DA variant they switched to eliminates the swapped first choices.

(when a student is assigned to a school, it is always to the best match
available for their position in the lottery)

------
PeterStuer
My main concern would be that there is no way to control the potential hidden
transactions included in the trades. I can well imagine less well of parents
or parents less concerned with education gambling on the most desirable
schools with the sole intention of making a buck on the trading aftermarket,
or overly keen parents with less inhibition putting severe pressure on other
parents to force a trade.

------
hedora
This seems like an extreme example of "good in theory" overriding "good in
practice".

The multi algorithm outperforms single, so run multi, then greedily swap
students at random until there are none that got each other's higher ranked
choice.

This obviously outperforms multi, and is fair, strategy-resistance be damned.

------
yread
They could only allow trading if you didn't get into your top 3 schools. That
way you couldn't really count on being able to trade and only the people who
were really unlucky could trade.

------
wolco
Does it not make sense for people to go close to where they live. It reduces
the carbon footprint and makes the school more local.

For the specialist schools have people interview, show there art/skill.

~~~
ricardobeat
Luckily most students in Amsterdam travel by bicycle :)

You can only signup for schools in your city area, which already restricts it
to a few km radius. For pre-school neighborhood limits apply.

------
tomohawk
Only 8000 students? In the US we have high schools that are that large.

------
Aaron1011
> Suppose, for example, that a student’s top choice school is hugely popular.
> But their number two to five schools are only slightly short on places. Then
> it could make sense to register for the number two school in the first
> round. They would have good chances to get into the second best school.
> Going for the number one choice is risky: if they don’t get in, they have no
> shot at any school in their top five anymore.

Why would not getting into the first-choice school affect the student's chance
of getting into any of their top five schools? The article's earlier
description of the Boston method makes it sound as though this wouldn't be the
case.

~~~
ricardobeat
Because the other schools are very likely to have been filled up already in
the first round.

------
Sniffnoy
I'm going to repost the same comment I made on /r/math:

> By trading places, students could get another shot at a place. At schools
> for which they already had a go in the lottery. This would give them better
> chances. At the expense of students that don’t (or can’t) trade. This is
> unfair.

This argument here is not correct. It's not at anyone's expense. The two
people trading both benefit, and other students are unaffected. Not everything
is zero-sum; not every benefit is at somebody's expense! (The strategy
argument -- that people had been explicitly told the system was strategy-free,
and it would be wrong to go back on that guarantee by allowing trading --
makes much more sense.)

This is an interesting article about social choice theory but the non-
mathematical parts seem to be making some implicit assumptions about
"fairness" that are, let's say, not exactly uncontroversial. And the argument
I point out above is just in error.

~~~
cortesoft
You are missing some key points - if they allow trading, they are going to
incentivize people choosing popular schools instead of ones they actually want
to go to. Since more people are going to choose popular schools in hopes of
getting a good trading asset, people who ACTUALLY want to go to those popular
schools are going to be less likely to get in.

Your assertion that it is an 'error' is only true if they only allow the
trading to happen this year (after the preferences were set), and not in
future years. The trades are only pareto-superiour if there are no future
decisions to be made; since this is a repeated game, allowing pareto-superior
trades this year means that next years game will NOT be fair (by their
definition of fairness).

I agree that their definition of 'fairness' is not objective, but it is one
they have decided to go with; they decided that the ability to strategize is
not evenly distributed, and so allowing strategy is unfair.

~~~
Sniffnoy
Yes, the incentives this sets up could be bad for subsequent rounds; that is
absolutely a real problem, as I mentioned. But this passage seemed to be
suggesting that trading, _in and of itself_ , harmed students who were not
involved in the trade, and that's not correct.

Notice it _explicitly_ says:

> This would give them better chances. At the expense of students that don’t
> (or can’t) trade.

But in fact those students are unaffected.

In subsequent years, as you say, it is a problem. But I don't see how to read
that part as anything other than denying that _when just restricted to that
year_ it is a Pareto-improvement.

You may say "well that's a self-evidently stupid claim; of course they're not
making that claim, because that would be stupid". But there's a lot of people
out there who really seem to believe in a zero-sum world, and are convinced
that when anyone's position improves, that means that everyone else has been
harmed. That Pareto improvements are fundamentally impossible. There are
absolutely people out there who would make that claim.

~~~
cortesoft
This IS a zero sum game, though. There are only x number of spots at each
school.

I agree that the wording of 'at the expense of' is a bit misleading, but I
don't think it is categorically incorrect. The idea of fairness can, by
certain definitions, even encompass pareto-superiour situation, if the
improvements are not distributed fairly.

I gave this example in another comment:

Lets say I have a cookie, and there are 10 kids in front of me who like
cookies. If I give any kid a cookie for any reason, it doesn't HARM the kids
who don't get a cookie; they are no better or worse off than if the cookie
never existed. However, suppose I decide to give the cookie to the tallest kid
- even though none of the other kids are harmed, this is still not a 'fair'
situation.

You can do no harm and still be unfair. Whether that is bad or not is
subjective, but it is still unfair (in the sense that every kid has an equal
chance at the cookie).

Of course, whether being absolutely fair is worth foregoing pareto-superiour
improvements is a moral argument, and there is no objectivly correct answer to
that.

~~~
Sniffnoy
I'm afraid the beginning of your comment contradicts your earlier statements.
Earlier you agreed that in that restricted situation, it is in fact a Pareto
improvement. However, now you are saying it is a zero-sum game. There _are_ no
Pareto improvements in a zero-sum game!

The rest of your comment just returns to the claim that the whole thing is
unfair even though nobody is harmed. But that's not the part I'm claiming is
wrong! The part I'm pointing out as a "straight-up error" is the part where it
denies that (in the restricted context of a single year where people didn't
know that trading would be possible) is indeed a Pareto-improvement. I'm not
making any argument as to the broader fairness.

I'm not sure we really disagree on much here.

~~~
cortesoft
Fair enough, I should probably have said 'seemingly pareto-superior' or
'pareto-superior depending on your definition of fairness'.

