Is it possible to register my children to attend the local secondary school?

Question

Or must I register them at a private school?

Answer 1

i think You are asking about any place in Mexico ?

Would be helpful to have some more info.
But regarding Your question: In Mexico You have the free choice to
send Your children to school or not. But if You send them to a school I would recommend a private school, as many of these are of a slightly better educational level.

Cost is from 200USD to 600USD for normal private schools.