Study breaks are not about replenishing willpower. They are about giving the brain some quiet time to organize the newly acquired information. Apparently, mental activity interferes with this organization process. I remember covering this 20 years ago in my psych classes. Researchers actually had one experimental group that reviewed an outline during their "break," another that took a nap, and another that was sedated. The sedated group actually retained the most information!

Now this is such common knowledge, it's hard to find the original research with a Google search. This makes me suspicious. Anyone have a reference?