Circular reasoning is when people try to argue a statement or point, by beginning with a premise presented as true or an affirmation (In this case, "If we all wear our school sweatshirts on Fridays, it will create a sense of unity"), and instead of proving this point, it simply continues asserting what it has said already but in another form (because they will help us all feel like a part of the school). As you can see in the sentence, both premises state the same but with different words, the second one does not say anything new nor relevant to prove why the first point is true.
This type of reasoning often follows the following pattern: "A is true because B is true; B is true because A is true.". A point leads to B point, and B point leads to A point, thus making it "circular".
