Current Students in Old Teacher Classes

Hello-

I have some current summer school students (9th and 10th graders) and they are still enrolled in a class from middle school.  How can they leave the class without contacting the teacher?  I could try to find her email, but I am not sure if she is still in our district (>400 teachers.). At least could I make my class as the default?  The assignments from the old class pop up and the students have to switch back to the current class.