What Judi said. And, you can do both ESY and credit recovery over the summer. It doesn't have to be either/or.
I think you really need to get with him, and develop a vision statement.
Your IEP is the roadmap--the vision statement is the destination.
You need to make sure that your IEP is pointing toward where he wants to go.
No child should fail a class, imo. But, if he can reasonably be expected to pass chemistry with the right supports, then his IEP is insufficient.
https://adayinourshoes.com/iep-vision-statement/