This is really a vent / cautionary tale for parents of not-perfect kids concerned about college admissions. In case you are not sure, if you have a kid, that kid is not perfect.
Our son is a senior at a top boarding school. He absolutely loved the school and was a leader on campus. Sending him to boarding school was a huge sacrifice (financial and otherwise) but he really wanted it. He was a bi-varsity athlete and a progressed from prefect as a junior to RA his senior year. Last December we got a call from him - crying so hard he couldn't breathe - that he was in trouble. He had smoked pot off campus over the weekend, and a student who was caught for other infractions said he had provided pot to my son. The deans showed up in his dorm room, demanded a drug test, and searched his room (which was clean). However, since he knew that he would be drug tested he confessed.
I can tell you that I never ever thought my son would do what he did and it was inexcusable. He was suspended and sent home. The humiliation was incredible. And deserved. For the rest of the year he is drug tested regularly and going to a counselor.
The consequences have been pretty far reaching though. For something that happened 100 % off campus, for which the school's only evidence was a voluntarily given drug test, the school sends a letter to all colleges where a student has applied to say that the student was subject to disciplinary action. On the common ap they then need to write an explanation of what happened, taking full responsibility. He was also stripped of his RA status. Being an RA was a huge time commitment and a major extra curricular to be highlighted on his college applications - until it wasn't.
Anyway, he had a pretty disappointing college acceptance season despite good grades, a near perfect ACT score, and very challenging curriculum, including Chinese.
I can't be sure that the suspension and the loss of RA status led to being rejected from some colleges, but if it did, it was due to an action that would never lead to discipline at a non-boarding school. One of our goals as parents sending our kids to boarding school IS a good college placement. I was glad that the consequences of his infraction were major but I have serious concerns about the impact they had on his future.
On a related note, one of the most common reasons for suspension is plagiarism. This does have a HUGE impact on college admissions. The issue at his school is that more than once a student has been found to have plagiarized when there are a few scattered phrases in a paper that match those (found using software) from another source - when it could easily have been inadvertent. Colleges don't care a ton about pot smoking on the weekend, but plagiarism can be devastating.
And, final note, star athletes found doing much worse have somehow had their discipline overturned.
4 years ago I was a smug mom 100 % certain that my kid would never ever do anything wrong and supporting the toughest possible discipline to keep out bad kids or kids who didn't adequately appreciate the opportunities of boarding school. Now having lived through this my attitude is quite different.