At this time, students cannot be rostered into multiple classrooms. If a student is rostered into more than 1 classroom, the student will only be associated with the most recently synced classroom. This will result in desyncing issues where it may appear as though assigning any lessons or assignments to the affected student is not working. If you suspect that this issue may be happening for specific students in your classroom, it's recommended that you resync the classroom in order for the affected students to be reassociated with your classroom.