In a Sudbury school students do not always learn in straight lines. A student might very well start learning a subject, stop and start a different subject, and then turn back to the first. In an example such as language, this could be beneficial. For instance, if a student starts learning Spanish, stops to learn some Italian, and goes back to Spanish, their knowledge of Italian could help them with their Spanish. A student could also start learning a subject which is viewed as more advanced than a subject they do not yet know. There is no particular reason a student shouldn’t start learning calculus before learning about U.S. history.