Accommodations are for all learning environments, no matter the level of difficulty of the classes. This myth your school believes is perpetuated by the very wrong idea that someone can’t be smart and struggle with school. The school is 100% wrong here.
I can’t give you specific areas of the law, but an educational advocate or attorney can. I’d seek someone to assist you with this in your area.
ADDitude Community Moderator, Parenting ADHD Coach & Author, Mom to teen w/ ADHD, LDs, and autism