Always been fairly melancholy kid. Serious. "Old soul" type of kid. Cerebral.
Family history of anxiety/depression.
He isn't on social media yet, so that's not really a risk factor.
Very active/athletic kid. Physically in-shape. Playing on his school basketball team.

He told me after practice yesterday that he thinks he is depressed. He said he was really happy to go to school that day, and especially excited to go to basketball practice, because he felt like he was getting better/improving. He has an hour after school before practice and he said that in that hour he got really sad, and didn't know why. I think it kind of scared/confused him. It's been rainy and dark the past few days, and I know he hates being stuck inside the school for 10 hours....

He was in a private school and partially home schooled last year, but he wanted to play school basketball this year so he went back to public school (where he had been for 7 years prior). The public school is massive. His grade has 1000 kids in 2 middle schools. I can't afford $40k for private schools in our area, which I think would be a better fit for him. Our state doesn't allow homeschooled kids to play school sports, otherwise, I would strongly consider this option.

What should I do as a parent?