Assign students to multiple setions?

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Is there a way to assign students from google classroom to multiple sections? For example, suppose we all do unit 1, then we start unit 2, take a break from it and start unit 4, then come back to unit 2? Would I just assign them one by one, assigning 4 when we take a break from 2 and then reassigning 2 when we go back to it? And would it have saved their progress from unit 2?