We've been to the same shool - not wrong but incorrect
We've been in the same school - correct
We've been in the same class - correct
We were in the same class/ school - ok
We were in the same year - ok
I have studied with my friend Anna - wrong
I have studied this essay - ok - meaning I went through all the details
mozesz tez powiedziec
He/She's my school deskmate - kumpel/la ze szkolnej ławki/ławy