"Memory Gaps" is the 1st episode from Season 1 of the animated series, A Kind of Magic.
Troubled by the sight of her darling son struggling with homework about Napoleon, Willow wields her wand (without his knowledge) to equip him with a prodigious memory, including a 20 volume encyclopedia set. Tom surprises himself in class the next day when he guilelessly produces an erudite speech.
Before realizing his prowess is his mother’s doing, Miss Tinker was convinced that he’s an exceptionally gifted child, which he tries to meet his parents. Panic-stricken, Tom beseeches his mother to un-do the charm. But Willow gets her formulas mixed up, loses her own memory, and ends up persuaded they’re still in Fairyland!