Consider getting them an eye exam.
I'm taking a class right now and couldn't figure out why I wasn't motivated and couldn't spend very long working on my studies before becoming distracted.
I'm usually a very good student.
Turns out I needed glasses. Now I'm back on track and it's so much easier to stay focused and motivated.
I know many schools do this but I just thought I'd throw my experience out there in case it helps anyone.