Nell and Woody are not exactly friends but they're not full on enemies. They don't exactly like anything about each other but they do occasionally talk, even if their words are mean. Nell is all about getting into Yale while Woody is all about getting a football scholarship so he can make something out of himself. The two are stuck doing a report together and end up in one of their usual fights. Their fight is in front of an Aztec God that forces them to get along. They wake up the very next day stuck in each other's bodies. Uncertain of what to do, they go about their day trying to be each other and try to go back to the Aztec God's statue and beg for him to reverse it back.
They realize the only way to get back in their own bodies is to understand and accept their current body and all of it's problems such as college, family and friends. They both work together as a team to get as far as they possibly can in each other's lives to set each other up for a great future and hopefully for great careers.
While spending so much time together and learning everything that each other's knows, the best they can, they start to truly respect each other and decide to make the other person's dream's their own dreams. Woody wants everything Nell want's and Nell wants everything Woody wants. If their future ends up being each other's, they want to honor that as a respect for one another.
Nell takes intense training from Woody to learn everything she can in Woody's body to help him get his football scholarship. Woody learns everything he needs to know to land Nell a spot into Yale. They both realize the little details about each other that matter and learn each other's hearts. They start developing feelings for each other. They learn why they were always in fights and it wasn't because they didn't like each other but because their families couldn't get along. Their families finally accept them as friends and possibly more.