Truman High

There has never been any mention of any schools that Sam and Dean have attended. In After School Special, it reveals one high school where the two boys went. At Truman High, Dean was in Grade 12, and Sam in Grade 9.

Dean's Experience
For Dean, school is a joke, and its just a way to spend his time while waiting for John to come back. He demonstrates this by not bringing book or anything else to class. He even calls the teacher "sweetheart".