Opt-out example Not choosing to subscribe to newsletters, unticking a previously ticked checkbox, not consenting to save personal details, rejecting the use of cookies, etc. are some examples of opt-out. E.g. Companies add an unsubscribe link at the end of their emails to let users opt out of emails.
Dear Principal Name, I wanted to let you know that my child, name, will not take part in the name the test this year. We ask that you make arrangements for him/her to have a productive educational experience during the testing period. Thank you for all you do.