When Joe and Matt are arguing over Debbie, Matt says that Debbie is the same age as Joe, which would make her 20 years old, and then Joe says that Debbie is 4 years older than Matt, which would make her 19 years old, so her being a high school teacher would be impossible due to the fact that she would be considered a college freshman or sophomore working without a teaching degree; she would be considered a student teacher.