Answer:
"This man, who was smart in school, has grown up to be unintelligent".
Step-by-step explanation:
Brutus is referring to a person who had access to education, attended school, but when he grew up he became an unintelligent, blunt, as if he had not studied right, forgotten everything he learned, or left school earlier.
For this reason, we can say that the best way to paraphrase Brutus' phrase is through the phrase "This man, who was smart in school, has grown up to be unintelligent", since paraphrasing means rewriting a phrase while retaining the meaning, but modifying the words.