Oh sweetie I am sorry your father said hurtful things. Just remember we parents lose it sometimes, I have certainly said things I don't mean or I shouldn't have. My daughter went to summer school 3 years in a row because math was just easier for her that way, it was all she had to focus on and they did all the work in class. By no means are you dumb and your father knows it.

Big hugs and I bet your Dad feels bad deep down inside, we just want our kids to succeed and not make the same mistakes we make, we forget that is part of the learning process.