What you don't see because it is invisible is that you've lost 5-10 minutes out of every hour of lecture time. And you don't realize that you're losing over 10% of the course you paid for because you don't realize what you could have had.
I say this both as someone with a tendency to arrive late, and as someone who has taught classes. Before I tried to write up lesson plans and saw what those interruptions added up to in lost teaching, my sympathies would have been with the student. Now they are not.
And in this you're assuming I'm the one arriving late and witnessing this? I certainly do occasionally, but I'm far from the worst in any of my classes.
As to missing those 5-10 minutes, if they're that valuable, the students will either arrive or miss out. That's their choice. And I wholly feel that way. I'll also point out that many many professors spend those first 5-10 minutes doing very little to progress learning, instead going over the previous class or simply getting ready. Not all, and I'm not accusing you of it, it's just that it's most certainly not the most valuable period in a class.
It's not your job as a teacher to make up their losses, it's your job to teach to the students. If those interruptions are taking teaching time away, it's because you are taking time away to deal with the interruption. That's your choice. All of the most effective lecturers and most valuable classes I've had have been taught by people who kept teaching, because these interruptions don't truly exist unless they're made to exist.
The student comes in late? Then they have to pick up from where they came in. You don't need to point out to everyone that they came in, nor do you need to tell them everything they missed - they'll ask other students (who they likely know) if they're interested. And with two exceptions in my 5 years in college thus far, I've never missed anything in the first 15 minutes that I couldn't pick up in 5 minutes from paying attention from that point on.
Those two exceptions were in art classes, when a demonstration was occurring. They couldn't rewind, and I didn't ask. It instead took me 5 minutes of experimenting and watching someone else go first, and then I was caught up.
If the teacher had made me go first, it'd have been identical to stopping everything just to berate me; it's only purpose would have been to see me fail, wasting class time, which is infantile at best. Sadly, many teachers feel this need.
The students don't know what they are missing. Were you aware that the few minutes at the start of class are the period where students have the best potential for paying attention? It is the place where ideally you should put the most important stuff that you want remembered. Not doing that is a wasted opportunity.
As for your lament that the time is wasted in review, review is actually one of the most important activities in the classroom. If you want long-term retention it is absolutely critical. Of course it is easy to not see the value of doing it.
As for my experience and part of why my attitudes changed, see http://bentilly.blogspot.com/2009/09/teaching-linear-algebra... for some of my teaching experience, and how I addressed these issues there. My attitudes only changed because I saw first hand how important that time was for learning.
Not that I blame you. When I only had only the amount of educational experience that you do, and like you only from one side of the educational equation, I too did not see how important these things really were. If you are like I was, then you won't understand unless, like me, you wind up experiencing the other side as well and thinking hard.
But even though you haven't experienced it, please pause in your certainty about the world long enough to accept that it is at least possible that, just perhaps, more experience would cause you to change your mind. Just as it changed mine.
> the few minutes at the start of class are the period where students have the best potential for paying attention
Oh, bull. Most are groggy, not thinking about the subject, and far from at their best. If you're an interesting teacher, their attention level goes up with time, not down. Learning in general exhibits a bell-curve-ish shape, not 1/x. Those first few minutes are best spent getting people back into the swing of what they're going to be learning about, starting the rise up that bell.
> time is wasted in review
Not saying it's a waste. Just that it's nothing that can't be picked up later by paying attention in class. That's kind of the nature of reviewing information - it's been covered before. Yes, the beginning is an ideal time to review, but that doesn't mean that it's impossible to make up, and by missing you simply can't learn anything that class period (which turning them away does mean). And remember, especially with a berating teacher, the ones that arrive late are the ones who want to learn. If they didn't, it's far simpler to just avoid the class. And interested students effectively come pre-primed for learning.
To sum up, my main point in all this: yes, arriving on time is important. But taking time to berate the student is the interruption, and is easily the least efficient way of dealing with the issue, and the most likely to alienate the student on both the subject and the teacher.
How, precisely, is this productive? It's just cutting them down when the teacher is feeling vindictive. If the teacher isn't aware of this, then they should really start looking at their motivations, because this is how it comes across. Unless they're a "repeat offender", in which case the class is probably on the teacher's side. It's simply downright mean, which is childish, which does nothing to further learning or respect for the teacher.
edit: I read your article, and it sounds like the sort of class I'd like. Most classes fail miserably at retaining info from the beginning, and the three-thirds setup sounds like a really good fit. The homework policy also appeals to me, as on-time is on-time, and very importantly it allows flexibility if needed. As a heads-up however, though frequent Q and A works with some professors, and when it does work it definitely keeps the class more alert, it's definitely not a one-size-fits-all solution. One of my gen-ed professors would be a perfect failing example of this; he'd end up waiting 10+ minutes for someone to answer his simple question, because everyone was sick of it. But he was hardly an engaging teacher.
I say this both as someone with a tendency to arrive late, and as someone who has taught classes. Before I tried to write up lesson plans and saw what those interruptions added up to in lost teaching, my sympathies would have been with the student. Now they are not.