How to delete a Mastery Goal for some students in a class...but not delete it for all students ?

Hello Sharon,

About the Mastery Goals, you should be able to edit them by following choosing the Edit options in the Actions drop down menu, in your Course mastery placement section:

If you are unable to do that in your class, feel free to submit a support ticket for our team to take a further look.

I hope this helps! All the best!