1. The boys are now at school.

2. The boys are now in class.
3. The boys are now in school.
4. The boys are now learning in class.
[Does #1 and #2 and #4 the same in meaning? What about #3? Is #2 the same as #4?]

1 and 3 mean the same thing.

2 and 4 mean approximately the same thing.

Students can be at school without being in class; they could be at lunch or out on a field playing soccer or in a gymnasium playing basketball, among many other things!