1;
Une école is for students aged 6-11 (I've heard some people group it 2-11) and is like an American elementary school. Un collège is for students aged 11-15 and is similar to a middle school.
Un lycée is like an American high school.
2;
à is to, in, at.
à + le is au.
à + la = à + la à + l' = à + l'
à + les = aux
(These rules are similar to de.)