We had both sets of grandparents upset when the idea came up. Avoiding the subject wasn’t realistic for us because the search was such a big focus for our family this fall and winter and we spend a lot of time with the grandparents. What ended up happening was that DC shared the viewbooks, course catalogs and other printed materials from the schools that were being explored. DC also showed them videos about the schools that were found on YouTube and Vimeo etc. Most importantly, our kid shared with them when my husband and I were not around why DC felt so strongly about going to BS. Being included during the search really helped them get used to the idea and also appreciate the opportunities that BS offers.
A grandma in her late 80s is probably well aware that her time on this earth is limited, even if she’s not mentioning that as a factor in her opinion. She also probably does not feel great about just “flying out” if she has to do that on her own. I’ll bet she will be fine with your son going to boarding school IF you take it upon yourself to make sure she gets to spend plenty of time with your son on breaks and however else you can manage it (i.e., helping her visit if you can).
MODERATOR’S NOTE:
As a reminder, when the OP asks a question, it is generally with the expectation that s/he will receive answers. Some answers may not align with the opinion of the OP and/or other users, and that’s fine. What is not acceptable, however, is throwing shade at a poster who expresses an opinion that is different. Numerous snarky comments deleted.
Our school also has a grandparents weekend. I concur with many thoughts here. It is hard to be away from anyone you are close to, and it’s no doubt harder if there’s uncertainty about health and longevity. With that said, if you can help the grandmother understand what you feel is important to success in today’s world, and then compare what is available locally and at BS, you might persuade her. One thing that hasn’t been mentioned is that BS typically have very few long weekends (and no in service days ) but much longer breaks to accomodate travel. This makes family vacation planning much easier. Perhaps you could think about some multi-generational plans for those long winter and spring breaks.
I can relate to this at many levels. Too many don’t live close enough to grandparents for the grandkids to become truly close. My kids are in that boat as I’ve moved around with work relocations no where near either set of grandparents. However, I grew up next door to my grandparents and my grandfather was my hero. I went to a boarding school starting in 11th grade. My oldest D started in 10th and just finished 11th.
I think your mother’s feelings are far from a parent trying to control an adult child or a sign of an unhealthy relationship between you. It’s natural grieving at her grandson growing up however it’s happening sooner than she expected.
I would ask you whether delaying a couple years is an option, not because your mom wants it but because your son could benefit. I was hesitant to let my D leave as a sophomore but there were reasons it was best. I still think junior/senior is better if you have access to a good HS for 9-10th. If the prep school is truly academically challenging, that’s a lot of years of hard charging and you can burn out before finishing undergrad. That’s from my experience as a boarding school student and my D’s now.
Is your son looking at starting freshman year? Does the school offer an option to start as a sophomore?
Thank you all!!! This has been so very helpful. I feel confident we can help my mom with this transition! Thank you!
I think time looks different what you are in your late 80s. She knows that if he leaves, she probably has little time left with him. And honestly, travel in your late 80s gets harder and harder, and could soon be pretty much impossible. I sort of see her viewpoint, I guess.
You are right about the travel, @intparent. My folks are in their early 80s and, although they are in good health and are totally independent, travel is much harder than it used to be. With aches and pains and other symptoms of aging, they sleep much better in their own home at night. I’m sure each year will just make it tougher.
When I read your original post, I thought you were asking for help with a parent who was questioning your parental decision.
Seems that I was trying to help you solve a problem you don’t have.
Best of luck to you.
I must have had brain freeze when I wrote this. My mom is 85. That is mid-80s, not upper 80’s. Good grief.
I know it’s still harder for her to travel than it used to be. However, she is going to Paris in August! The funny thing is she never admits she doesn’t want my son to go to boarding school because SHE will miss him. She concentrates on how much I will miss him. She’s not wrong. 
Thanks again everyone for the ideas.
@PossiblePrepMom - that’s what we did too. He did a five week summer session and loved it. That was it. Good idea to have your mom go with you to take him. Hopefully, she will see what a great experience it can be.