When I was 14, I wanted to have sex more than I wanted anything else in the world. Let me be clear: I did not want to have sex because the media told me I should or because my friends were doing it or my boyfriend was pushing me. I wanted to have sex because my body was flooded with hormones whose entire reason for existence was to make me want to have sex.

I was so desperate for assurance that my desire was normal, that it didn't mean I was turning into a hopeless slut who would be pregnant at 16 and dying of Aids by 20, that I actually put my faith in a Health and Development class. I was seriously disappointed. Female sexual development, according to my teacher, was an embarrassing, uncomfortable process, but one which would allow me to one day experience the miracle of motherhood. I learnt about ovulation and menstruation. I learnt that the appearance of pubic hair signals an increase in androgen levels, and that tender breasts and swollen nipples indicate a rise in oestrogen. I also learnt that testosterone was surging through my body and might cause me to feel 'strange'.

Boys would not feel 'strange': they would feel horny. They would be distracted by sexual thoughts and feelings. Their genitals would engorge with blood for no reason at all. They would feel a deep, low-down ache, which could only be eased by sexual release. They would have erotic dreams from which they would wake to find they had messed up their sheets and pyjamas. I am a boy, I thought, my face hot and my thighs pressed together.

Girls in many UK classrooms today are likely feeling the same mix of curiosity, bewilderment and shame. Although all secondary schools are required to include sex education in the curriculum, the content and nature of the lessons is up to individual schools to decide, and many decide to stick to basic biology. But sex in the real world encompasses much more than the penetration of a woman by a man for the purpose of procreation, and this is especially true for teenagers who engage in a far wider range of sexual experimentation than most adults. Not for them three minutes of kissing followed by safe and efficient grown-up intercourse. Teen sexual activity is about hands and mouths as much as it is about genitals. It is about curiosity as much as satisfaction, about figuring out what feels good and what doesn't, what you want and what you don't.

Teenagers are not doing all this adventurous touching because the media is saturated with sexual images or because they lack moral guidance; they're doing it because they are sexual beings and touching is what sexual beings do. We can tell them to 'just say no' and we can refuse to provide information about sex, but we cannot take their sexuality away. It is part of them and it will be expressed.

My own experiences are instructive. According to my parents, friends and health teacher, only unloved girls with low self-esteem let boys use them for sex. And using it would be, because boys were only after one thing, and if you gave them that, you would never see them again. Fine, I thought, let them use me. Bring it on.

But the teenage boys with one-track minds evidently went to a different school, and the men who coax innocent schoolgirls into bed must have done their seducing in another town. Every day I stepped out into the world exuding sexual heat, and every day I was ignored. Each time I willed someone to touch me and they didn't, I shrunk just a little.

After a year or so of this, with my body under the influence of a couple of million years of evolutionary drive, and my head full of chilly scientific facts, I decided that I could trust to the beastliness of men no longer. I made friends with a gang of slightly-older-than-me boys with long hair and tight jeans and jobs pushing trolleys and washing cars. I did not sleep with these boys; they were my mentors.

We hung out in a pizza parlour whose owner allowed us to drink beer as long as we didn't throw up inside, and I listened to their stories of conquest and defeat. When the shop closed, we hit the streets and I watched these stumbling, reeking boys pick up girls. When there were no girls around, they coached me in the art of seduction. They taught me how to identify an easy target, how to convert a 'no way' into a 'maybe', a 'maybe' into a 'yes.'

My plan was to become so good at seduction I would never be rejected. I was willing to trade my good reputation for sexual fulfilment, but not to be seen as desperate or pathetic. This plan failed miserably, of course. I was rejected frequently and cruelly; the boys who did accept my come-ons were usually inexperienced, clumsy and selfish; my reputation was far worse than I deserved and far harder to deal with than I had anticipated; and, more than once, I found myself way out of my depth.

This is exactly what parents fear, I know. That their daughter will fall in with a bad crowd, be whispered about in school hallways, written about on toilet walls. That their little girl will find herself in a locked room or isolated parking spot with a man who neither knows nor cares that the girl beneath him is clever and talented and underage. That she will be used and cast aside, promised the world and given nothing but a reputation.

Looking back I am horrified at the risks I took with my health and safety. Far from protecting me from sex and its consequences, the just-the-bare-minimum approach to sex education left me incredibly vulnerable. Of course I knew that I could get pregnant or worse, but I was so ashamed of my desire, and so grateful for whatever action I was getting, that the last thing on my mind was avoiding infection or insemination. Besides, I had been taught that the only really safe sex is no sex, and so I thought there was no point bothering with protective devices that could fail anyway.

I wish I could say that teenagers today are better informed and prepared, but a recent study by sexual health charity Brooks indicates staggering ignorance amongst teens. Only a third of sexually active teenagers use condoms regularly, and about half don't know how emergency contraception works. More than half think only women get chlamydia, and a quarter don't know that sexually transmitted infections (STIs) can be transmitted via oral sex. The consequences of this ignorance are grave: STIs are on the increase amongst UK teenagers.

The government should be ashamed of these results, as should all parents and educators who, out of ideology, embarrassment or ignorance, fail to properly inform young people about sex and its consequences. What teenagers need to be taught - what I wish I had been taught - is that sexual desire is neither unnatural nor harmful, and that although acting on that desire can be dangerous, it need not be. To this end, teens need detailed, accurate information about how STIs are contracted and prevented. And they need to learn that not only is it OK to say 'no', it's also OK to say 'yes', with the right person and the right protection. And teenage girls, who are surrounded by images of sexually provocative women yet told constantly that 'good girls don't', should be told that their desire, which is just as insistent as boys', is a positive force, that good can come from following its call.

This knowledge is the happy legacy of my reckless, confused teen years. Through sheer luck I came through physically unscathed, and although most of my encounters during this period were disappointing and humiliating they were compensated for by the rare but brilliant moments when I understood why I was driven to this, moments when I caught a glimpse of a person who my teachers and parents and girlfriends either didn't see or didn't want to acknowledge. I caught a glimpse of myself as I wanted to be.

· Should sex education be more honest? Write to the Observer Review, 3-7 Herbal Hill, London EC1R 5EJ or email review@observer.co.uk