I was 14 at the time of this event, although I had started masturbating long beforehand. I was at school after hours one day as my parents were busy and unable to pick me up until later in the day. I went into the toilets thinking I would play with myself for a little while when I heard a moan coming from just the other side of the wall. You see, in our school the toilets are a little block with male on one side and female on the other, and just a wall in between. This means that at the top there is a nice sized gap.
The moaning got louder from the other side and I could tell that whoever it was, obviously thought everyone else must have gone home and so they had decided to treat themselves. Of course because there is a gap I thought I may as well try and get a look, just to see who it was and what exactly they were doing. Plus I was a 14 year old male so of course I was going to look. To my surprise it was a girl who we will call Claire, one of the most attractive girls in my year, with not a scrap of clothing on, leaning against the door fingering herself. Because of her position her face was tilted slightly upwards and she immediately saw me peeking over the wall. She immediately grabbed her clothes, put them on and walked out of the toilets. Thinking I had been well and truly caught I went back down to the ground of my cubicle, but after what I had just seen I had to have a wank anyway. I had just removed my pants and boxers and started stroking my now fully erect member when I heard a knock on the toilet door. Looking through the crack I saw that it was Claire!!!
I opened the door, half covering up and she walked inside and shut it again. Saying she thought I needed a better view, she once again stripped and started masturbating. Of course it didn't take me long to remove my clothes once more and I just sat there watching her as my penis grew ever larger. She was moaning really loudly by now and I reached over to feel her wetness, causing an even loader moan. Assuming that was good I started rubbing my hand over her pubic region (not really knowing what I was doing) until she pushed me away, saying she was about to orgasm. Having never seen a female orgasm before I paid close attention as that overwhelming sensation took hold of her.
I found myself so aroused by all of this that almost without even realising my hand had started to stroke my cock once more. I was getting faster when she bent down and pulled my hand aside. She then reached over and started pulling on it for me. She must have had some experience at this kind of thing because she was very good at it and had me at the edge in no time. She leant in even further so her tits were directly above my dick and just gently finished me off. That was by far the biggest cum of my lifetime and it went all over her lovely tanned chest and ample breasts.
Unfortunately she then looked down at her watch and saw the time, obviously realising that she was meant to be going and very quickly put back on her skirt and t-shirt before rushing off, leaving me in the toilet all alone. It wasn't until I went to leave myself that I noticed she had left her underwear behind, mixed in with the pile of my clothes. I have until this day kept them hidden away in my room as a lovely reminder of all that took place that afternoon.