I am a high school teacher and am looking for a position at a different school. I was recently accepted and enrolled in a master's degree program in my field and intend to begin coursework in June. I don't want to be misleading, so I was thinking of putting it on my resume with the explanation "Recently admitted, anticipated start date: June 2018." Is this a good plan, or should I leave it off?
Only if it compliments your teaching, i.e. I have recently been enrolled in a master's degree program in my field to help gain a deeper understanding to compliment my ability to teach X
If it's irrelevant to your current role, i'd as an employer question your motives for doing this, and be concerned about your long term career within that institution along with you commitment to the role over your personal education
Since it fits inside your field, I would say that yes, you should have it in your resume. Not sure what your location is, but I've heard of jobs/locations that require you to at least be working towards, or have, your Master's in order to keep the position. This shows that you are already working on this requirement and have been accepted to a program.
Secondly, it also gives your perspective employer an idea of other responsibilities that you have. Some jobs might find that risky, but I would think that as an educator, they will find that you pursuing a higher degree is acceptable.