Matilda (novel)
Matilda is moved into a higher class, and Miss Trunchbull is eventually replaced as headmistress. Matilda is happy with the challenge, but soon finds that she's lost the power to move things with her mind. Miss Honey guesses that the cause could be that Matilda had nothing to use the strength of her mind on when stuck in a first grade class, which allowed her to use that extra mental power to move objects. But now that Matilda’s brilliant mind is being challenged every day in her new class, she has no extra power left over to affect the physical world.