The answer to your question can be found in chapter three of Madeleine L'Engle's A Wrinkle in Time.  Calvin and Meg are at Meg's house, and Meg's mother is getting dinner reader.  Mrs. Murry suggests that they finish up their homework before the food is ready.  Calvin says that he does have some math homework, and the mother suggests that Meg help out.  Calvin doesn't think that Meg will be able to help, because he is several grades ahead of her.  

Mrs. Murry smiled. "Why don't you get Meg to help you?"

"But, see, I'm several grades above Meg."

"Try asking her to help you with your math, anyhow," Mrs. Murry suggested.

It turns out that Meg is really, really good at math.  She knows a bunch of short cuts, because she and her father used to play math games together.  Apparently, Meg is not only good at math, but she is also a good teacher as well, because Calvin finally begins to understand his math homework.  

"Well, we have to do it their way. Now look, Calvin, don't you see how much easier it would be if you did it this way?" Her pencil flew over the paper.

"Hey!" Calvin said. "Hey! I think I get it. Show me once more on another one."