1. Go to Students>Groups.
2. At the top of your classroom list you will see the name of your classroom.
3. Click on the classroom name and you will see a dropdown of all the classes loaded into your school account.
4. Tick the other classrooms you need and the students from those classes will appear in your list.
5. The final step is to move the students into your group list.
Please click here for more information on how to set up your Groups.