Two different groups of students use the same classroom every day.
Literal
Every-day same classroom [object-を] two [possessive-の] different students' groups [with-で] are-using [explanatory-のです].
のです adds explanatory nuance — the speaker is explaining a situation, not just stating a fact. 異なった is the past/attributive form of 異なる ('to differ'), functioning as an adjective meaning 'different.' ~たち pluralizes 生徒.