The problem is not always raw ability
Parents often see a teenager who seemed to follow in class and then falls apart alone during homework. That gap is real. A 2019 meta-analysis on math anxiety and performance confirmed a robust negative relationship among school-aged students.
In practice, rising anxiety can disrupt working memory, decision-making and the ability to hold a solution path together. It is not the only cause of weak results, but it is a real and common one.