Hi BKD. If you are happy to give a few details that might help with more specific advice and stories. 11 is a tough age. If your DS is in a bricks and mortar school and has reached the top of the primary grades, that can be a time when interest in school can slip. Things can pick up when the challenge of High School kicks in. Just the process of High School and more independence can help reignite interest in some kids. But, they need to be challenged as the superficial charge from changing schools doesn't last.
We found with DD 12 that not being challenged leads to all kinds of problems with self efficacy and self concept. Over coming that is hard work but is possible.

Thank you so much for posting master of none, made me want to cry. It's so true! We have to parent and it is hard work and tough love and we doubt ourselves and what we are doing. Well done. We are walking a similar path.

Big hugs BKD. a few books that you can get on Amazon including kindle versions are:
Why Bright Kids Get Poor Grades and What You Can Do About It by Dr Sylvia Rimm
The Underachieving Gifted Child: Recognizing, Understanding and Reversing Underachievement by Del Siegle
When Gifted Kids Don't Have All the Answers: How to Meet Their Social and Emotional Needs by Jim Delisle and James Galbraith. Good chapter on underachievers versus selective consumers!