Dunce - A person who takes more time to learn something, especially dull person.
Open Word Class - Noun
1. While others were solving the fifth sum, this dunce boy was in the second only.
2. I fail to understand what this dunce boy keeps doing in the house, he fails in every exam.
3. I would say that you need to work over this child; he is a dunce fellow, and takes longer time to perceive a concept.