When you are viewing the classroom that the student currently is in, using your mouse, hover over that student. You will see two icons appear.
The second one is for moving the student.
Click on it and you will be taken to a form where you can select the classroom (homeroom) to which you want to move the student.
Submit the form and the student will be moved, and you will be returned to the homeroom from which he/she/they came.