To remove a student from your class:
Click on the dropdown menu carat next to the class name to display the student list
Click on the bubble to the left of student name to select the student
Select "Remove" from the menu at the bottom of the screen:
*Note: This will just make it so they no longer see or can access your class' formatives. They still have a Formative account, and you can have them re-join that class or another class at any time! If you have a student rejoin a class, all of their data will repopulate in your Tracker.