It is brother vs. brother today on "Are You Smarter Than a 5th Grader?" when Nick and Drew Lachey enter the classroom and take the test!

"They are doing their celebrity week and it is for charity, so what better to do than make a fool out of yourself for charity?" Drew tells ET.

And Nick adds, "We are fairly competitive as brothers. Most brothers are. We are taking this seriously to see who comes out on top."

Comedian Jeff Foxworthy hosts the all-new half-hour version of "Are You Smarter Than A 5th Grader?," airing Tuesdays on MyNetworkTV.

Drew proved he had all the right stuff when he won the mirror-ball trophy on "Dancing with the Stars," but he is not so sure about this.

"I don't even remember what I studied, much less the answers," Drew says about his time in fifth grade. Then he adds, "I was best in gym."

Nick says he was good in science, but not so much when it came to arithmetic. "I hope there aren't any tough math questions," he admits.

"There is not betting going on, but bragging rights," says Drew. "If he wins, he will rub it in for five years. If I win, I will rub it in for the next seven."

Nick is playing for Feeding America; Drew is playing for Autism Speaks.