When multiple students from the same HS apply to the same college, are they competing just against each other? The Dean advises. https://www.collegeconfidential.com/articles/would-princeton-admit-all-five-applicants-from-my-high-school/
Well, Princeton enrolled 34 from Lawrenceville over the last three years. Based on Princeton’s typical yield figures, they may have accepted over 50.
https://www.lawrenceville.org/page/academics/college-counseling
There are still “feeder schools” that send atypically large numbers of seniors to certain Ivies each year, but even these figures are way down from what they were in eons past.
They might admit all or none or some number between. What you can’t predict is which apps they will find compelling (so don’t try). 
It may surprise you who gets admitted from that pool. You can’t know everything in their apps - rec letters, ECs outside of school, ethnicity/family origin info, essay content, legacy status, etc. All you can do is put your best app together, then go on to focus on the rest of your list of schools (reach, match, safety) so you are sure to have choices in the spring.
The top private/boarding schools do send consistently high numbers of students to Ivies each year. The numbers are falling compared to 10 and even probably 20+ years ago. If you really look at year over year matriculation rates for many schools they are extremely consistent–consistency in a market with such variables suggests agreements.
Agree with Sally that even at the traditional feeder schools, the number of students being admitted to Ivies has been dwindling in recent decades as a result of the value placed on geographical, racial and SES diversity by these institutions. For non-feeder schools, it’d be extremely unlikely that all 5 get admitted. If these 5 applicants all have similar excellent academic stats, it really comes down to the individual unique achievements and traits that’d make a difference – if at all.
Even at the feeder schools, it’s unlikely that Princeton accepted everyone who applied, though.Yes, the acceptance rate is probably well above the average, but I doubt there are many cases where a highly selective college has accepted every applicant from a particular HS. But since we aren’t AOs, and since we have not seen the 5 applications, none uf us can sat definitively.
But for the vast majority HSs, isn’t it true (to a large extent), that you are competing with your fellow classmates for the same highly selective colleges?
^ It depends. For example, at Cornell, students apply to specific colleges. An engineering student is not going to be competing with a Hotel student. That said, if everyone from the same high school is applying to the same college, then it would be less likely that they would all be accepted (at least in my experience).
Only in the sense that all the applicants from the same HS are on a level playing field in terms of course offerings, school ECs, etc. But the reality is that not all of them will avail themselves to those resources or have the same stats. So I agree with @Sally_Rubenstone that the fact that all are from the same HS is not a deal-breaker all other things being equal, but all other things are never equal.
@skieurope @momofsenior1
I agree and see your points, but if the premise of diversity of geography were true, then for the majority of HSs, highly selective colleges just could not, mathematically speaking, accept more than two students from a giving hs, (in fact under most situations none from a given HS, which is why students from the same region are competing with each other for highly selective colleges too), regardless of major/strengths. No?
Dartmouth accepted 2 students from a class of 50 at my kid’s HS - the only 2 who applied. This attempt to read the tea leaves is futile. Do your best app, have a solid list, and keep moving.
I’m not sure that “the vast majority HSs” even has in reality enough qualifying applicants to vie for “the same highly selective colleges.” Perhaps there are enough academically qualifying applicants, but that’s not enough without non-academic excellence or unique quality to go with it to be truly “qualifying.”
At my S’s high school, there’s always been several “academically qualifying” students each year but among them only one gets selected by Princeton about every other year on average. The reality that academic excellence alone isn’t enough explains why the kid who graduated 6th in his class gets to walk through the Princeton’s FitzRandolph Gate while the kid who graduated valedictorian gets admitted to none of these highly selective colleges. We see that all the time nowadays. This is why the student who posed the original question regarding competing against other applicants at the same HS needs to stop worrying about others. There’s really no competing with one another; the competition is with one’s own self.
I never agreed to that premise.
I will agree that Princeton wants to select as strong a class as possible and that they want diversity. But I do not believe, at least for domestic applicants, that there is a mathematical formula in place for geography.
Here’s the reality - Princeton will offer acceptances to approx 1950 applicants. There are 37K high schools in the US, so most of them will have zero acceptances.
For the Class of 2022 at Princeton, there were 0 students admitted from the state of WY, SD, ND and MS. So, echoing @skieurope’s point, there’s no mathematical formula in geographic consideration in admissions.
Re #14, while Princeton enrolled no students from those states, I’ve not seen information regarding acceptances from those states.
Yes, it’s possible that some applicants from those states had been offered admissions but chose another school. The point is that, by “geographic diversity,” it simply doesn’t mean that the class has to be filled with students from EVERY state.
Of course there is no mathematical formula nor requirement to fill each class with students from all states, but every TT school wants to boast about it has students from every state (better yet, country), and to say there is no competition from the same HS/region by highly competitive students (not just academics) is no different from saying there is no racial quotas (whatever the PC terms used by each school).
No, they don’t. They have more than enough applications from every corner of the globe that they have no need for this marketing ploy. With the exception of MS, these states are all low-population states, so there may have been no qualified applicant. No top school is going to take a less-qualified applicant from SD just to say they did. Clearly you feel differently, but since debate is not allowed here, I’m moving on.
I have seen MIT/Caltech and Ivy admissions recruiters set up meetings in Cheyenne WY, , and the meetings often attract 95-100% Colorado and Nebraska students, in Cheyenne Wyoming! Its very difficult to recruit from Wyoming, but top universities do seem to try. Cheyenne is near both the CO and Nebraska borders.
I have seen MIT admit six students in a year, from one or two Colorado high schools, Those two high schools appear “feeder” high school for MIT, and a few of those students, two that year, attended Harvard or Princeton as I remember.
Strange things do happen on any given year with admissions. The " odds" are broken in admissions at times.
Which is why it makes sense to apply where you want to attend, regardless of other students in your high school.
I have seen a Math Olympiad get rejected for instance and land at a public university. He was top 16 in the USA in math and did not apply to enough schools, assumed he would get into his first choice, but he did not get in.