My first teaching job was as an English Instructor in a major university, and the only classes I taught were Freshman English.
The first semester, on a particular occasion, I hadn't prepared a lecture for my first class, so I assigned them to write an 'impromptu theme' in class. While they were writing, I sat behind my desk and gazed around the room and there was one young girl, probably 17-18 years old, who was a real knock-out. Dark hair, deep blue eyes, breasts that pushed her blouse out very nicely, and she was sitting so that I could see partway up her thighs. I felt myself getting an erection just looking at her, and I put my hand in my pocket and fondled my penis for a while. I had to stop, because I felt myself on the verge of cumming, and I surely didn't want to mess up my trousers with a big wet spot for everyone to see. When the class was over, I beat a hasty retreat to my office, and behind its locked door, I pulled out my cock and masturbated into my handkerchief, all the time picturing that young girl.
But, this gave me an idea. At home, I took a razor blade and slit the seam at the end of the trousers pocket on one of my older suits, making a hole large enough to pull my erect cock through and into the pocket, and I got a packet of condoms. I couldn't very well give that class another impromptu theme to write right away, so I checked out another one of my classes for likely subjects. There was a blonde fully as pretty and well-stacked as the brunette in my first class, so I decided to focus on her. Before my next meeting with that class, I put a condom on my cock.
While they were writing their themes, I started looking at the blonde, sitting in the same way as the earlier girl, and I got an instant hard-on. I reached into my pocket, pulled my erection into it, and then began stroking it. It was very nice, because after 'milking' it a few times my 'pre-cum' lubricated the inside of the rubber and made for a very enjoyable physical sensation in my penis. I took my time, since I had nearly 50 minutes to gaze at the girl and work myself up to orgasm, and I guess I brought myself to the verge three or four times.
Finally, it looked like she was about to reach the end of her theme, so I squeezed my cock, moved my fingers up and down on it, and then shot a load into the condom. I hoped nobody was watching me closely, because I was sure I'd gritted my teeth almost to the breaking point and that my face must have turned a beet red. Anyhow, it was one of the most intense orgasms I'd ever experienced up to that point.
This was a practice which I intended to repeat on many occasions, and the next semester I was determined that I was going to have a bevy of beautiful young girls to look at while I masturbated in my trousers. Since I was in charge of registering students for Freshman English classes that semester, when a guy or ugly girl came up to register in one particular class of mine, I'd tell them that section was closed and put them in someone else's section. But if a young beauty wanted in, the section was wide open! As a result, I wound up with 24 students, 16 of them among the most beautiful girls on campus, eight of them were nominated for 'Class Beauty,' four of the others were elected as 'Sweethearts,' and a couple of years later I saw still another one in a 'girly show' at Las Vegas.
That semester, I had a ball! They wrote a lot more impromtu themes than the students in any of the other Freshman English sections, for sure! The last one they were assigned before the end of the semester, I was paying very close attention to one particular girl whom I had watched while masturbating on more than one occasion. I kept staring at her, and then I noticed that she was looking up at me quite frequently. I didn't want to seem too interested in her, but I couldn't keep my eyes off of her. She was wearing a fairly short skirt, and occasionally when she moved, I could see the white crotch of her panties. A couple of times, when I saw her panties, I looked up to find her looking at me, and the thought entered my mind that she might be showing me her panties on purpose. But, naw! She wouldn't do that, surely!
As the class hour approached its end, I couldn't help but stare at her, because I wanted to be looking at her when I came. As my orgasm approached, I saw her look up at me and stare straight into my eyes, and I thought, 'My God! does she know what I'm doing?' Then, to my amazement, she crossed her legs and, while still staring at me, began to swing her foot back and forth.
The way she was looking and moving her upper leg made me absolutely sure that she was masturbating, herself! I didn't know what to do, but I was on the verge of cumming, and at that point I didn't really care if she knew what I was doing. I know my eyelids must have drooped when my orgasm began, and at the same time, I saw the foot on her swinging leg suddenly curl back as far as it could go, and the muscle in her calf tighten into a knot. The swinging of her leg increased in speed, and I saw her grip her pen tightly in her fist. Her eyes closed, and I knew that she was cumming. I thought the load I shot might very likely be so strong that it would burst the end out of the condom, but of course it didn't.
When her leg finally stopped swinging, and my own orgasm had run its course, she looked directly at me and smiled. I wonder, to this day, if she knew that we had just had mutual orgasms, and I think she did. I think she'd caught on to what I was doing earlier in the semester, and maybe that turned her on enough to make her want to join in the fun.
I kept up this process for years and years as a college professor, and mid-term and final exam times were something I looked forward to eagerly.