Complex sentence: The commons areas, gym, band room, and vocational classrooms weren't completed until a few years later, prior to that students had to eat sandwiches in the media center, and play basketball games at the middle school's gym.
Split into simpler sentences: The commons areas, gym, band room, and vocational classrooms weren't completed until a few years later. Prior to that, students had to eat sandwiches in the media center, and play basketball games at the middle school's gym.