One day after school I was helping the Biology teacher work in her back room. Ms. Smith was an attractive middle aged woman with big boobs who always wore short skirts and showed a lot of leg. She was preparing slides for the next days lesson and I was putting things away.
With a disappointing moan she said that the slides were no good. I asked what they were and she said human sperm. Then she asked if I would be willing to give her a sample. I thought about it for a minute and shyly said ok. She said good, take off your clothes it is better if you are totally naked. While she made sure the class room door was locked I stripped.
When she returned I was standing there with a half a hardon. She looked and asked if I were shy. With that she sat down in front of me her skirt rode up exposing lots of leg and a surprise. I could see her pussy and my dick sprung to attention. I started stroking and as I watched her I could see her pussy getting wetter and her nipples hardening under her blouse. When I blew my load I think it was one of the largest loads in my life.
I will always remember that day and my contribution to science.