If you're a person who loves to be comfortable, who loves to sleep, you might easily get tired while wearing a sweatshirt during school. Baggy sleeves could simulate a feeling of a blanket around you, making your brain think you're ready to sleep, causing you to be tired. Also, while writing, dragging baggy sleeves against a desk, per say, could slow you down to an extent. What do you think?
While warmth may increase the chances of a student feeling sleepy in class, I believe it is up to the teacher to keep their students engaged in class. And what about when the school is cold, here in Canada often times the heaters aren't turned on in the school for over a month after the temperature starts to drop, I've seen students wear winter jackets in class and still get their work done. I'm even less likely to get anything done if I'm cold. As of right now, my school is so cold I could go outside and be warmer than I am right now. I think it's up to the student if they wish to succeed in class that day. We can't blame an article of clothing for the lack of work that gets done. Just my opinion though.