If you divide a dough between classmates and everyone home a piece do you have to give challah
A dough that has a shiur of Challah, but the dough is destined to be split, is exempt for separating Challah. This is called “Isa Lechalek”- a dough that is meant to be separated. A classic example of this, is a teacher who makes Challah with her class with more than a shiur, but she is going to give each girl a piece of dough to braid or some dough to take home to bake. The Halacha is that she cannot take challah from this dough unless she saves a shiur of challah for herself. If she saves a shiur of challah for herself, she takes challah like any dough, however, it is preferable to take the challah before the dough is actually split. If the dough was already split challah may still be taken.
Mishna Challah 1-7, Y:D326-2, Bach ibid, Shach ibid-5, Mishpatei Eretz 2-2, 20, 26.