No advice other to say I’m sorry. 11th grade English at his private was hell for my son and worse than college courses DH and I took. He got through it but it was a struggle the entire year. Do what you can and keep plugging away. Have him keep talking to the teacher. For mine, it was the writing and the details.
If it’s any hope, 12th at his school is nothing like that and much easier. We don’t know if it’s the course or if he has an easier teacher.