Hi, my name is Megan Tuck and I'm studying my A-levels at college. Last week was my eighteenth birthday and, until then, I had been a virgin. However, I loved to masturbate and would often do it three or four times a day.

Anyway, my story begins on the day after my birthday. It was a Monday and I was back at college. My first lesson was double biology. I've always enjoyed biology, especially the reproductive organs, but the subject really started to grab my attention when we got a new teacher this year.

Her name was Miss Chasterty and she was stunning! She was in her early thirties and had a very pretty face - blonde hair, hazel eyes, glistening lips and a cute button nose. The rest of her body didn't disappoint either. She carried a few extra pounds, but only enough to make her look extra curvy, and she had a large firm ass.

The bell rang on Monday morning and it was time for my biology lesson. I strolled in and sat down on a stool. Miss Chasterty hadn't arrived yet and there was chaos in the classroom. A paper airplane suddenly hit me in the back of the head. I turned round to see Brogan, one of the popular kids, sniggering at me. I got up and started giving her a piece of my mind, and just as I did so, Miss Chasterty appeared.

"Miss Tuck, what do you think you are doing?" she yelled. "Stop shouting at Brogan and sit down. I will see you in my office at lunchtime."

And with that, the biology lesson started. It was a long lesson, but I was secretly looking forward to being on my own with Miss Chasterty later.

The bell rang for lunch time and I headed for Miss Chastery's office. I knocked on the door and was told to come in.

"I'm very disappointed in you, Megan. I thought you behaved better than that."

"I'm sorry, Miss, it will never happen again," I pleaded.

"Well I hope it doesn't, but I can't let you get way with this. You're going to have to be punished," she replied. As she said that, she scooched her chair closer and rested her elbows on her knees so that I got an eyeful of cleavage.

"What are you going to do to me?"

"Well, I'll give you two options," she responded, getting even closer. "You can have detention for a week, or you can fuck me."

I threw myself back against my chair, totally in shock at what I had just heard, but my pussy was leaking just thinking about it.

"But, Miss, you're a teacher."

"Well, I won't tell anyone, and it could be classed as some practical biology work on the female reproductive system."

I didn't need to hear anything else and gave a nod with a big grin across my face. She immediately got up, locked the door and drew the curtains. Then she put her leg over my knee and sat on my lap, facing me. Our lips got closer and closer until we were kissing passionately. Her hand went down my top and started teasing my fully erect nipple.

I let out a soft moan as I felt my panties becoming drenched. My top soon came off, as did my bra and panties. She got me up and laid me across the office desk.

My legs instinctively spread, exposing my soaking, pink, cleanly shaven pussy.

She rubbed my clit and I jumped in delight as she slid a finger into my virgin vagina; the first finger other than mine to have entered that territory. After a short while of finger fucking me I felt like I was about to explode, but just before I did she pulled out. She then dived open mouthed onto my female parts. It was something I had never experienced before and I was in sheer ecstasy. Seconds later my volcano erupted, and the lava sputtered all over my teacher's face.

"How was that?" Miss Chasterty asked.

"The best thing ever, Miss!" I managed to say in between in heavy breaths.

"Okay, now it's your turn. And please, call me Helen."

She wriggled out of her clothing and swapped places with me. I started off the same as she had done, rubbing her beautiful clit and then inserted a finger. She was moaning softly, but I didn't think it was good enough so I put in another finger. She moaned louder. A few seconds later I put in a third finger. She screamed with pleasure and so in went the fourth finger.

"Ahh, mmm, oh yes, Megan, just like that."

I started finger fucking her faster now.

"Okay, Megan, I want you to fist me."

"What?" I said in disbelief.

"I said I want you to fucking fist me. Hurry up you, little slut!" she replied.

In bent my thumb and I pushed my wrist in. She screamed so loud I was surprised nobody heard us. Then her muscles clenched around my fist and a wave of excitement spread through her as she came to orgasm.

"Keep going!" she demanded.

I pushed my hand in further and further until it was almost up to my elbow, then I opened my fist. She started panting and wriggling around uncontrollably. I pulled out fast and my mouth was quickly on her pussy, just as she had done to me. She exploded into my mouth with her sweet juices.

I climbed on top of her, sucking one of her breasts on the way up, and lay there with her for a while.

"That was so amazing," she said. "You're so good at that."

"Really, I've never done it before," I replied.

"Well, I'll definitely be giving you a detention more often," she said, and we both started giggling.

Then she climbed on top of me and rotated herself 180 degrees into the 69 position. I started lapping up her pussy as it dripped onto my tongue. She did the same to me, but then jammed a finger into my ass. It was like an electric shock that almost made me cum instantly. I reacted by biting hard onto her clit and squeezing my nose into her anus. We both started squirming and had a synchronised orgasm.

"Oh, I'm so going to miss this, Helen," I said.

"So am I, but I have an idea. Why don't you come round my house a few nights a week for some extra biology help?" she responded, with a cheeky wink.

And so we both got dressed and went back to the rest of the day at college. But that wasn't the last I saw of Miss Helen Chasterty's beautiful, sexy body!