Braun attended Granada Hills High School in Granada Hills, Los Angeles, California. He was a four-year letterman on the school's baseball team, and three-year team captain and Most Valuable Player (MVP). He played shortstop and pitched through his junior year. As a sophomore in 2000, he recorded the highest batting average of his prep career (.456), while posting a .654 on-base percentage (OBP). During his junior year, he hit .421, with a .668 OBP. Braun capped off his high school career by batting .451 as a senior, with an OBP of .675, and breaking the school record for career home runs with 25.