Home school parents have many stories of this happening to their children. Our daughter became convinced that she was terrible in math because she missed a couple of weeks at the beginning of a school year and became confused. This problem continued for several years as she had trouble with math, was put in a slower class, had less expected of her, and did even poorer.
We finally decided to homeschool her starting in 7th grade. Three years later, she had one remarkable week where she completed 4 weeks of math lessons in 3 days — simply to get the opportunity to go to the beach for a weekend. And her scores are always higher when she is working faster because she concentrates more.