Leaderboard rankings are specific to the classroom in which the students are assigned. By changing a student's classroom, the class they are being placed into is considered new to the student, therefore the student's prior classroom rank will not reflect in the new classroom.
Example: Daryl is in Classroom A, and is the 1st Place Point Leader for his assigned classroom, school and state. The following day Daryl is assigned to a different teachers classroom, Classroom B. When Daryl logs into Imagine Math to check his Point Leader status, he notices that his name is only ranked in 1st Place for school and state, but not his current classroom. This occurs because though points do move with the student, classroom rank is based on points earned while completing work within the currently assigned classroom.