Yes, of course it happens. When I was in 8th grade the second time I sat next to a boy named Justin who was two years younger than me in science class, so I was like 15 and him 13. I will never forget the fact he always wore really soft pants that showed off what he had. He had nice balls but a short dick. Anyway we sat in the front just feet away from the teacher's big desk. We both wore denim jackets with hoods and we would hang them on the back of our chairs and make them spread out so as to hide the sides facing each other. He would unzip and I would play with his dick all day during class. One day he put his head on his hand which was propped up on the desk by his elbow, covered his mouth so the teacher couldn't see but I could, and without making a sound moved his lips to say "I am cumming" and then I felt his cum start squirting and running down my hand. He sat on my right so I was using my right hand. He laid his head down on the table and quietly put it away without too much movement. I then put my hand to my mouth and ate his nut, which freaked him out because he wasn't gay, just horny. He still let me play with him all the rest of the year, but he never came again. Looking back on it though I am almost certain the teacher could see and just didn't know how to handle it. The teacher died of cancer when I was 19.
There was another boy too. His name was Kris and it was the same year. He was a very small kid who hadn't grew much yet. Where I just felt sorry for Justin cause he was unpopular and got picked on, I was in love with Kris. He was so cute. Blond and blue eyed and of German decent. In art class it started by admitting to each other we jerked off and then I admitted me and my friend who came over on the weekends to stay the night would give each other blow jobs. He asked me if I ever swallowed or let him cum in my mouth and I told him that the other boy couldn't cum, which was very true and we found out later it was a medical problem, but he did have a huge horse cock. The next day we had an assembly and went to the hall and he sat next to me. The lights were dim and I took a chance. I laid my coat over his lap, which he looked puzzled at me, then I started petting him thru his pants. He got hard and without hesitating took his dick out. He had a dick of about five inches (he was 13) and nice bush, which surprised me as I had seen him in gym with his shirt off and he didn't have any arm pit hair. He cam in about 5 minuets. When I ate his he smiled and made a kissing sign with his lips. From then on he came to stay the night every weekend and he was the first person who I ever kissed and made out with and we told each other we loved each other. This was in the early 90s.