ちょっと分からない・・・ I don't quite understand...

I was marking tests yesterday, and I noticed that even on the second trial, one student didn't manage more than 4 out of 20. This student isn't the best student in the class, but usually she does better than that. I mentioned my concerns about her to the English teacher.

Me: Did you see K's score on the test?
T: Yes.
Me: I was a little surprised. Is she ok?
T: Yes, she's ok. She goes to juku (cram school) so she is busy with that.
Me: Ok...
T: Yeh, so she doesn't have enough time to do her school work.
Me: ...

That doesn't make sense to me. Especially the fact that it seems acceptable for a student to not do his or her school work and subsequently fall behind, all because he/she is too busy with cram school work. Hmmm.

Even after three years, Japan surprises me sometimes.