I have a son who was depressed last year in 4th because of the lack of challenge in school. He didn't have behavioral issues, and was already accelerated, so that might have made the school more willing to accommodate. But we made radical changes to his curriculum this year (online math, a mentor and different LA) and he's back to normal.
But in contrast to what the others are suggesting, I give my son mental health/recharge days when he needs it. He's extremely busy out of school with a sport and several academic extra curriculars, so I understand how he can get burned out. Even with his changed curriculum, he's not anywhere near the top of his challenge-level, so I think it's fine for him to sit out a day if he needs it. And just knowing he's allowed to do that made a huge difference in his moods. He now knows there's an "out." I trust him not to abuse it and he's only taken 2 days this year, but I expect he'll take more later in the year.
