dunce
A person who is called foolish or slow to learn.
A dunce is someone who is slow to learn or understand things, though the word is often used as an insult rather than a fair description. You might hear it in old books or movies: “Don't be such a dunce!” means “Don't be so slow to catch on!”
In old-fashioned classrooms, teachers sometimes made students they considered slow learners wear tall, cone-shaped dunce caps and sit in the corner. This cruel practice, thankfully abandoned long ago, was meant to shame children into trying harder, but it mostly just humiliated them.
Today we understand that people learn differently and at different speeds. Someone who struggles with math might excel at writing. Someone who seems slow to understand one subject might be brilliant at another. Calling someone a dunce ignores these differences and judges them unfairly.