This took place starting when we were in seventh grade, about 1961 or so. Names have been changed to protect the not-so-innocent.
I don't really recall how it started, I think it was on summer time sleep out with friends. There was a group of us guys, about five of us, who spent most of our summer time together. We would take turns having 'camp-outs' at each others house, maybe two to three times a week. Sometimes it would be all five of us, sometimes just two or three.
One night it was just Ron and I in a tent in my back yard. We were talking and soon jacking off. By the end of the summer every single night would be a jacking session, sometimes even 'helping' each other. We kept up our clandestine meetings throughout the school year whenever we could.
It was now summer before our eighth grade year and we were staying at Chris' house for the night. Chris had a pool and we often went skinny dipping in it. This one particular night while skinny dipping and jacking, we were pretty daring and were jumping from the roof of the house into the pool. What we did not know was that two houses away a group of three girls were watching this group of naked boys with boners get up on the roof and jump off.
One of the girls was the twin sister of one of our group and she confronted him about it the next day. This apparently led to the two of them sharing some masturbation times together.
About a week or two later Mike told us what had happened with him and his sister. We all got boners but everyone of us called him a liar. In our minds there was just no way a guy and a girl would masturbate together, yet alone a brother and sister. Little did we know!
In order to prove he was not lying he offered to let us watch them do it together. Long story short, we saw it happen just a few days later. There was one requirement from Janice, Mike's sister. We all had to get naked too. Let's just say that there was a great deal of cum spilling in that bedroom that afternoon.
Janice told us that her friends would also like to see the same thing. By the end of the summer, three of her friends joined the five of us.
Over the next few years our group of eight grew to an informal club of about 15. We would jack solo or help each other. Any person was welcome to help or join any other.
Oh those were fun times! Since those days I have never had any other group times.