How do i overcome my anger when my mom insults me?

Okay, whenever my report card comes in the mail my mom has to see it.I don’t mind what gets me mad is that if i don’t have an a+ in all my classes ,she starts yelling at me and telling me i am a disgrace and then she compares me to the son of one of the ladies she works with.He is a nice boy and all but my mom and his mom are constantly trying to compare us to see who is smarter .I try to write my feelings down but then she looks at it and gets even more mad and i get furious that she went through my stuff.I really need an answer!