Does your son understand that his classes and grades in high school are a large part of what allows him to attend the college he would like to attend?
Also to be on any teams and clubs he will need to maintain passing grades.
We always told our daughter we would rather have her make a B in honors than all A. This would mean she was really having to work for her grades, because she was being challenged. We just wanted to do her best.
We also reminded her, SHE would be doing the work. We were not going to be keeping up with her work etc.
I do believe you need to speak with his teachers and find out exactly what is going on with him in the classrooms and where are the lower grades coming from.
In my husbands case he is very ADHD and hated the busy work.. He could look at math problems and tell you the answers, but he hated having to "show his work".. SO he would get terrible daily and homework grades, but pass the tests and exams.
Even worse.. He parents would make sure he did his homework.. but he would not turn it in!!!
He ended up doing well on his SAT and so he got into a great college.
Speak with his teachers and see what the suggest and then have a sit down with your son and see if he can understand the dilemma right now.
You do not want him to be bored in classes, but you also need him to understand he will need to do the work. He will miss out on amazing opportunities in the honors classes. Our daughter had some incredible teachers, attended great plays, museums, dissected all sorts of animals.