my 2 cents on the examples I shared above:

I personally know one kid, who is really smart and talented.

If these kids started in NY city of CA, they might still be top (or in the 1st tier) students in maths there. If they could accept the fact that after transferring, they were not top students anymore, and continue to work hard, they would be able to catch up the top students. Most kids most likely got confused and frustrated. Help from parents is very critical. 

This is just like some friends posted previously here: in college, during the first 1-2 years, students from "lagged" states (like the one of my state) may need some extra efforts to match the students from CA, NY city. Afterwards, once they are used to and learned the lesson, they are able to do just as good as those other students. The critical thing is that college students were much mature than a junior high or high school students.

I agree w/ ur suggestion.