I grew up in a small town in rural Alabama. I'm not sure how old I was when this happened, but here's my experience.
I believe I was 12 and playing JV football. Unknown to us, the coach arranged for a doctor from a town about 10 miles away to come do physicals on us. (Later in high school this doc became my family doc, but that had nothing to do with this physical - just a consequence of living in a rural area and not having many choices.)
After practice we always had to shower - required by the coach. Usually when practice was over there would be about 25 boys fighting for one of the 12 shower heads, each one taking a 2 minute shower and then getting dressed, hoping no one noticed our stiffies.
This particular day the coach stopped practice half way through. We throught we were getting a break but he told us to go to the lockerroom for a team meeting. When we got there, he introduced Dr. Moore to the team and said that he'd be giving us our physical exams. The coach told us to shower and line up outside his office. A couple of boys had already had a physical so he wound up excusing them.
That left about 22 or 23 of us standing naked outside the coach's office. Some boys had a towel around the waist, some were nude. The coach would call in 4 boys at a time and the doc would do the checkup on all 4 at the same time.
I'll never forget the guy behind me in line poking my ass with his dick. He and I had JO'ed a couple of times, but we weren't suck buds or anything like that. I think he was trying to prevent the other guys from razzing him aboug having a hardon, so he just pushed it up against my ass. However, looking around, about 1/2 the boys were at least partially hard and some were totally hard.
The coach called my group into his office. The coach took the towels from the two boys who had them on and the doc did the exam. He did do a hernia exam and all four of us got hard when he did that, but he didn't do a rectal exam. (Knowing how sensitive my ass is now, it's a good thing he didn't - I probably would have shot a load in front of him, my coach and my teammates!)
After the group of four was examined, we were free to go.
The next year the school required each boy to go to a doctor and bring in a form from their family doctor, so that was my only experience with a group physical exam.