"IQ levels" are almost impossible to measure objectively, excluding medically identified learning disabilities. Reading comprehension difficulties are less a function of fluid intelligence (commonly called "IQ"), and more so environmentally induced. Examples of this are, but not limited to:
- Instability at home
- Lack of parental involvement
- Prejudice, explicit or subliminal, by school staff.
- Hunger and/or fatigue
- Dejection resulting from some combination of the above.
As far as optimizing teaching techniques, I can only say I believe there is not an easy answer for that. People are different, kids do not operate as adults would, group dynamics sometimes benefit with change and other times not, and I would be hard pressed to think that personalizing to the extent possible would be a bad thing.
In short, IMHO there is no universally applicable solution to the teaching problem domain. Which is likely why so many of us hold teachers in high regard and remember them so well.
EDIT: preposition and indefinite article use.
0. Make the "dumb"/ADD/poor kids feel inferior. Paradoxically, a percentage of people who were told they would never amount to anything often are driven to prove others wrong, and over-achieve later on. Props to them.
1. Make the "smart" kids feel on-the-spot and ashamed that they're embarrassing the "dumb" kids. Also, pulling kids out of class to make them arrange triangles with a timer (IQ "tests"), dropping them into music lessons like trained monkeys and skipping grades because they are expected to be omnipotently-capable might be a bit stressful.
Maybe it would help if there were more striations of progress levels, or with technological assistance, more custom individual edu plans (IEPs) that could maximize each child's progress acceleration vector... do away with collective punishment of outliers by making classes stick to the mean average. Also, if teachers got more involved (maybe with social workers and other support resources) to make sure each student is safe, fed, treated humanely at home and has their needs met so they can learn, that would be awesome.