I am thinking ahead for my next child, who may or may not be interested in BS in the future.
This child’s main EC is one that takes a lot of time and is not offered at any BS. Part of this child’s decision to attend BS will likely be based on whether child plans to continue this activity in high school or not, as we have no expectation child could continue this EC if attending BS. (I am intentionally not specifying the activity.)
My question is whether it would be a significant disadvantage for the child’s main EC through middle school to be one which child can not use to contribute to BS community.
I believe child is learning a lot from the activity and enjoys it, and can probably apply some of what child has learned to new activities at BS. In addition, child has many interests outside of this main EC but currently does not have time to pursue these interests due to main EC.
But on the other hand, I can see AOs wondering what child will add to their community since child’s participation in other activities will be fairly minimal.
Does anyone have any personal experience with this?
It happens. I know figure skaters who have to find local training with arrangements made independent of BS resources. For that matter, there are a number of BS kids who are way above the level for the school to support in some activity whether it’s music or a sport or dance or whatever,
My son was on a high school sports team to be part of the team, the school. His training, however, was private, not through the school. One sees this with top golfers, tennis players, swimmers, etc.
So, it would mean making special arrangements for the activity on your own and coordinating it with the school. Paying for it separately too
I have known a couple of kids who did something really well and at a high competitive level and outside of BS. (Gymnastics, Irish dancing). I think AOs will want to know how, if you are going to continue, you’ll make that happen. Definitely easier if you live nearby.
AND they want to know that you’ll still be part of the community and be able to handle the work load.
Ime, it is far easier to customize your time around a not-in-school sport or activity at a private day school than at a BS. But if you can envision how you would do this and are committed to it AND will not be asking the school to make a lot of accommodations for you, I think you’ll have a fair shot.
@damon30, I do not want to specify the activity.
@cptofthehouse, while it may be somehow possible to arrange for child to continue the activity while attending BS, outside of school, child and I both feel that if child wants to continue this activity in high school, child would be best served by going to LPS or possibly a local day school.
If child applies to and chooses to attend BS, it will be with the intention of no longer doing this activity.
I am more interested on how it may affect admissions decisions if the child’s main activity has been on the child does not plan to continue at BS, and child has minimal other ECs because most of the focus has been on one EC that will not be continued at BS.
Again, it is possible that child will be able to transfer some skills developed through this activity to BS activities and it is possible child may make quick progress in other ECs that child is currently participating in at a low level, once main activity is dropped and child has more time to devote to the other activities. But child will not have a proven track record in any ECs that BS offers and won’t be able to demonstrate how child will contribute to the BS community in terms of activities in the application process.
In what I have seen, a BS is a community and would most value activities that support that community directly. They want musicians for their choir and orchestra. They want swimmers for swim team and basketball players for that team. However, it is still early for most children to have emerged in their skills so it isn’t these schools don’t have as much self interest as the colleges.
So I suggest that your DD talk/write about this activity in application interviews/essays and how it can lead to other contributions to other ECs. These schools do like a diversity of talent too, so yes, skills in anything are of interest.
Our son had exactly two ECs, and Choate did not offer either. He was pretty concerned about that, but he was able to start a club for the one and presided over it the four years he was there. He had to write up a business plan and justification for the equipment and space needed, and the school funded it. From what I can tell four years post graduation, the club is still running.
The other EC was Boy Scouts. He contacted a troop local to Choate to see if he could join them while he was in Wallingford, and they were happy to accommodate, but there was no time in his BS schedule to do so. Instead, he worked a plan with his home troop to maximize his breaks and summers to ensure he could complete his Eagle rank before turning 18. He made it work.
If you’re talking about a competitive sport that requires a large investment in facilities and equipment, that may be another ball of wax but, if there is any way your child can take the reins and bring the EC to life at BS, it will benefit both your child, the community, and your child’s college application. 
My kiddo had 2 main EC’s (no, not including golf) that were not offered in BS. For our experience, there were both athletic EC’s and a performing arts EC. One was very time demanding and very competitive at a national level. We made a decision to drop that EC because we could not afford it if we went to BS and also risk of physical injury. For the second EC, we took a drop into a lower level of competition and now competes only during vacations or in the summer. Yes - going to BS can involve sacrifices of all types - in addition to the financial sacrifice.
We do know students at BS whose parents drive (or have car service) them every weekend to competitions or for outside travel teams. We see this with hockey, soccer, and tennis. This is very $$ and takes an enormous amount of parent participation. It’s an added stress to your kid’s life adjusting to the academic rigor of BS and social adjustment. Also, it takes those students away from the BS community for a large chunk of the weekend (eg after Sat classes through Sunday night). Why send your kid away to school then?
My kiddo did write about the EC’s for the apps, sent videos, photos (kiddo’s actual real-life head attached to self in photo) and discussed these experiences during interviews (eg, attending the ODP training centers, competing internationally, competing against adults, training 8 hours per day or more in the summer, maturity and responsibility). Did having an EC or playing a sport that was not offered at the school impact admissions? No - kiddo got accepted into 7 well known “alphabet” schools . Maybe because this was all, but one, AO realized that this applicant was a multi-sport athlete and did PA? I hear coaches and trainers say they like kids who are athletes - not necessarily one specific sport… and/.or an artistic student, yet not one specific instrument or endeavor. Have your kid write about/talk about how the EC experienced changed him/her/themselves.
Be prepared: Giving up even one EC has resulted in much emotional wrestling and physically missing the sport than could be imagined. This is coupled with the big change of going away to school. Think of everything that is in that “pot to stew” (self esteem, social connections, physicality, coaching, achievement). It is NOT easy on your kid!
Try to find a balance and see if you can hang onto at least one aspect of the EC. Giving up a sport that is not a “lifetime” sport is very difficult…that is yet another reason we like golf for the kids. Even if you don’t play in school, there is plenty of time when you get older ?!
I know a kid who was a tippy top gymnast and decided not to go forward with it and attend BS. The decision to quit was really well thought out and articulated, and acknowledged leaving that “family” behind. I suspect this student came across as quite thoughtful and intentional with good plans for using the time, the work ethic, maturity, perspective, etc that come from doing something at that elite level. Also know that this student has thrived at BS. Note that through admissions, this student was already defining herself as a former gymnast.
I’m going to guess that it will matter how much identity is tied up in that EC as well. Schools don’t worry if kids struggle with some parts of the BS experience but are genuinely concerned if they are completely unmoored from everything that can sustain their confidence and self. Or if they seem to have plans that are incompatible with the school.
Put differently, my sense is that schools are open to kids who are self-aware and prepared to engage. An EC the school doesn’t offer can prepare them for that (a la student above) or can insulate them from that. It’s really about where your kid is vis a vis the EC.
@Golfgr8 I feel like your kid’s situation might have been different because while she had ECs not offered at the schools, she also had very strong ECs that definitely were offered at the schools. I think the situation is very different when all of your ECs are “irrelevant” to the school community.
These are 13-year-olds. Many (most?) of them have no particular major extracurricular activity - certainly not at the level of your child - and don’t know yet what they will pursue in high school and college. My son, for instance, had never played squash before high school. He is on his college team. His trumpet playing may have helped him get into BS - they were desperate for trumpets that year - but he gave it up after two years to have room for other classes. My daughter had to give up a high-level voice program and her local theater opportunities. Many BS students change activities for various reasons. Schools want kids who are open to trying new things and who will become full participants in the community. They don’t necessarily need to know what the student’s appointed slot in the community will be. 
I don’t think THE activity matters. What matters is that your child has activities. The schools are trying to find out what makes them unique as a person. Yes, they want to fill out their team rosters and have kids who do arts and all the rest. But schools also know that kids can learn new things, drop some and some may even be great at something they pick up at BS.
Some good points are made above regarding various trade offs. For most BS kids, they have more activities than time and need to winnow down their activities at BS. And if kids decide they want to do something not offered by the school they will miss out on social time and various BS activities.
My daughter and I both gave up significant ECs to attend boarding school. I was skiing competitively and chose a BS that at that time had no team - just a club. I wrote on my application that I would be interested in starting a team and then cried the first time it snowed. I taught others how to ski in ski club and life moved on. I also played field hockey which was more of a hook for schools. In this century, My dd was a nationally ranked competitive rock climber when she applied to boarding schools. None of the schools had the type of walls she required to train and at that point she was climbing over 20 hrs a week and competing year round in multiple states. It was a tough choice to walk away. While she had other leadership positions, this was her only sport. I think her commitment and her discipline were noted by the schools but her EC was not a hook. In retrospect I wish we had followed the example of the gymnast above and made a clean break and used “former” on her applications but instead we had conversations with schools about possibly working with us to continue to train at BS which we quickly realized was pretty impossible to do. My DD did mourn the loss her first semester but then she made the JV ice hockey team and now she is playing Ultimate Frisbee in college and climbing some too. She also ended up loving theater and ran several diversity clubs. She feels she would have missed out on all of this if she had stayed home to climb but she was never a kid who wanted to only do that one thing - those kids will be in the Olympics for the first time in 2020! To sum up, schools see this as a character strength and a plus but not a hook. My DD quickly met dancers,figure skaters and gymnasts at BS who had all given up pursuing their sport at elite levels to attend BS.