Final answer:
A 2001 Nickelodeon study found that the average ten-year-old has a mental age of around ten years old, according to cognitive and developmental tests.
Step-by-step explanation:
A 2001 Nickelodeon study showed that the average ten-year-old has an estimated mental age of around ten years old. This study likely used various cognitive and developmental tests to assess the mental abilities of ten-year-olds. One test mentioned in the provided information involves drawing a diagram from memory, which is typically drawn correctly by a child of ten years old. This study provides insight into the cognitive development of ten-year-olds.