* M.Ed. (Elem. Ed.): This is probably the most common and clearest option.
* M.A. (Elem. Ed.): Some institutions might use a Master of Arts degree.
* M.S. (Elem. Ed.): Some institutions might use a Master of Science degree.
* MS in Elem Ed: A less formal but still understandable abbreviation.
When using an abbreviation, it's always best to spell it out in full at least once earlier in the document to avoid confusion.