It is very rare that someone goes straight to grad school as their billet upon graduation. Two athletes in 2021 did get grad school billets, but that was primarily due to the covid rules allowing them to compete during their year of grad school. One went to Rutgers and I don't recall where the other went. I believe in the case of those two I had heard that the schools reached out to them and offered them a full scholarship to compete (instead of the Coast Guard funding their school). Usually, going to grad school would be something you applied for later after a tour or two. At that point, I assume that your grades during school would still have an impact for getting into the school you wanted, but it would be up to the Coast Guard to decide if they were going to send you.