First, it's important to note that as a parent you are perfectly within your rights to refuse to let your children take this test; there is no legal consequences to you or your children by the state in doing so.
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.
What do I need to do? Write a letter or email to your principal letting them know that you intend to “refuse” the tests on behalf of your child.
Your email can be short and sweet. Here's an example: “I would like to opt my child NAME out of MCAS or ACCESS testing this year. Thank you.” Go to citizensforpublicschools for more information on your opt-out rights. You have the power to decide what is best for your child.