Cancelling Activities for the Whole Class
Navigate to the lesson you want to cancel.
Scroll to the bottom of the page where the Student Submission box is.
Click the cancel button on the Student Submissions header:
You will be prompted to type the phrase "Delete Assignments". When you've done so, click on the Cancel Assignment button to finish cancelling it.
Cancelling Activities for Individual Students
Click on the button next to their name as seen below:
After clicking on the button, you will be prompted to typw the name of the student. After you've done so, click on the Cancel Assignment button to finish cancelling it.