Do you mean ter tell me," he growled at the Dursleys,....

“ Do you mean ter tell me," he growled at the Dursleys, "that this boy—this boy!—knows nothin' abou'—about ANYTHING?"Harry thought this was going a bit far. He had been to school, after all, and his marks weren't bad."I know some things," he said. "I can, you know, do math and stuff. ”

J.K. Rowling

From : Harry Potter and the Sorcerer's Stone