Have your student log in to their school Google account using their school email and password
Have your student go to canvas.washk12.org
Have your student follow these instructions to generate a "pairing code"
Log out of your student's Google account, or on a separate device go to Step 5
Click "Parent of a Canvas User?" near the top right of the login box on the screen
Create an account, and use the pairing code your student created (Note: codes expire after 7 days or one use)