Does rest really improve concentration, and ability to self-regulate class work?
Yes, and I would argue that it does not even have to be complete rest. In my experience, being lazy to the extent of professional indolence tends to put me out of practice at doing homework. Spring break was a busy week, full of spending time with friends, visiting places, and going on adventures. Yet, since I returned to school, I have had more success motivating myself to do homework than I had for weeks before the break. I hope this trend continues.
It's also possible that my increased self-regulatory ability has simply come from the fact that I've spent a week not thinking at all about my self-regulatory ability, in which case, it's about to come to an abrupt halt.