Miss Honey may be taken with Matilda, but she also doesn’t want to make her other students feel bad—she’s responsible for educating all of them, after all. Notice too that Matilda doesn’t seem to be showing off. It’s just a fact for her that she can perform mental math and read everything. This shows that Matilda is humble, which, within the world of the novel, is part of what makes her a morally superior character.