[socrates1998]

>average they would do better the next year because of reversion to the mean.

I don't think it works like that. Students who do poorly often do WORSE the next year. They tend to get more and more behind and eventually just drop out.

The only way to reverse this trend is to identify them for more academic instruction, like an extra math or reading class.

Even then, it often doesn't work. It's really really hard to turn a low performing student into even an average one.

"Reversion to the mean" has no meaning when you are talking about one student from one year to the next.

[collective-intl]

It's definitely not the pattern that doing worse once snowballs inevitably into future years, at least not on average, because students' scores still always assemble in a nice bell curve.

I think a better model is that you are not likely to stray too far from your "true" ability, since even if you forgot (or missed) everything from previous years, you could still learn a certain amount in just one year (and probably you remember some things).

[socrates1998]

I never said it was doing worse once. And it absolutely does snowball. A student who is a poor reader in grade school often falls further and further behind.

And grades are not "bell curved" shape. That's ridiculous. Do you know the average grade at Harvard for every class, it's an A.

That's definitely not Guassian.

Man made things like income, grades, stock market prices and home prices are not "bell shaped".

They are heavily skewed one way or another.

I would recommend you do a little research before making such patently wrong statements.