Okay im looking for a fic (im almost 100% sure it was a oneshot) and in it Mr. Schue decides to add an extra Glee rehearsal on a day the Cheerios practice. Kurt, Santana, and Brittany (the only Cheerios of the club at the time) tell him that they can't because Sue would kill them if they missed a practice. Schue decides to hold the rehearsal anyway and make the three Cheerios say after where he tells them that they have to choose between Glee and Cheerios. He believes that they will defiantly choose glee over the Cheerios and he is excited to win over Sue. The next day (i think) Kurt, Brittany, and Santana come to glee in their Cheerios uniforms, obviously not choosing glee, and Kurt acting as their spokesperson (Brittany and Santana are crying) explain to all the gleeks whats going on and they all understand.
I hope this is enough information. Thanks so much!