We recommend that students stay in the same course and time session throughout the season so that the coaches in that session can grow to know the student's strengths and improvement areas in as much detail as possible. Additionally, students often take multiple sessions to begin to work together well with partners and to enjoy working with students from different schools/backgrounds.
If there is really no way to move forward in the current session and there are openings in other courses of the same level, then yes, students can change if it suits their schedule more conveniently.