Matilda has the very special power of telekinesis, which is the ability to move and manipulate objects using only the mind. It takes some time for Matilda to develop this power, but once she does, she puts it to good use. Arguably the most positive way in which she does this is by making the wicked Miss Trunchbull so frightened that she suddenly leaves the school and her home behind, never to be seen again.
Matilda uses telekinesis to levitate a piece of chalk while Miss Trunchbull torments the class yet again. Using the chalk, she writes a message on the board, purportedly from the ghost of Miss Honey's late father Magnus, that threatens Miss Trunchbull with dire consequences if she does not leave her house and her money to Miss Honey and get out of town. Suitably spooked by the experience, Miss Trunchbull does just what the "ghost" demands and takes off. This might not seem like a positive use of Matilda's powers. But this is Miss Trunchbull we are talking about here, so Matilda's little prank is more than justified.