It was another gloomy day at Hogwarts, despite it being past the middle of March. The sky was dark with clouds that occasionally sprinkled the land with rain, and the Dementors' presence made everything much colder than usual. Harry was sitting in the common room, trying to recall any happy memories that would help him cast his Patronus, as Professor Lupin had taught him, but he just couldn't recall any. Even the Weasley twins didn't seem happy.
Hermione plopped on the sofa at his side. Since she had made him lose his Firebolt – the present he got from some unknown source – he had some mixed feelings towards her. He knew she meant well, only wanting to protect him, yet giving up that formidable broom... He also felt some stirring in his loins whenever he looked at her. Despite her prominent front teeth, she was quickly becoming a real beauty, and her body was filling nicely, giving her a very enticing womanly figure.
"A knut for your thoughts," she said teasingly.
Harry felt his face getting warmer. "I was trying to recall happy memories, as Professor Lupin taught me."
"That's all? Why are you blushing, then?"
He felt even hotter. "I was just noticing how nice you look..."
Hermione blushed at his compliment. "I'm still no competition to most other girls, beauty-wise." He heard some bitterness in her voice.
Before he had time to think of an answer, Professor McGonagall came through the entrance to the common room and looked around. "All third year boys, please come with me," she said sternly.
"We've done nothing wrong!" he heard Ron protest from another sofa, where he was trying, not too diligently, to see what homework he needed for the next morning.
"I didn't say you did. Just come with me. I think you may enjoy it." Harry thought he heard some mischief in the teacher's voice but dismissed the idea. His head of house would never do any mischief, he was sure.
He looked apologetically at Hermione, who just waved him away with a knowing smile, before he joined his four dorm-mates and followed the Professor.
Harry recognized the way they were going and didn't really like it. They were going in the direction of the Hospital Wing, a place he had spent too much time in and was not looking forward to another visit there. Yet that was where they were going to. The Professor opened the door and urged them in.
They found five girls – all sixth or seventh year, Harry couldn't tell – waiting there, each clad in only a dressing robe, so it seemed.
Professor McGonagall looked approvingly at the girls and then turned to the boys. "It is the school's duty to prepare you for life in more than one way. This time, you're going to learn some very important aspects of life, and I dare say you're going to enjoy your lessons very much. Each of you will be escorted by one of these girls to a partition, where you can study all you need. I believe you won't finish your studies before curfew time, so you should stay here until morning. Make sure to act properly and learn well. I'll get a report about this by tomorrow evening. Have fun!"
She promptly turned around and left the teens alone. Harry had no time to think about what it all meant, as one of the girls came and grabbed his arm, leading him to a partition and closing it, once they were in.
"First thing you should learn is discretion. I'll now cast a silencing charm on the partition, as the first step," the girl told him.
Harry could hear the other girls speaking with the boys. Although most spoke barely louder than a whisper, he could still hear the noise, even if he couldn't discern the words. His escort, or teacher – he wasn't yet sure what to call her – waved her wand at the partition and whispered a spell. A moment later he could no longer hear the others. The silence was so deep that he thought he could almost hear his own heart beat.
"I'll teach you that spell in a moment," the girl said. "While this may seem good enough, it isn't. You also need at least a good privacy charm as well. The silence charm will not allow sound to pass through the charmed object, but it can still travel above or around it. The privacy shield takes care of that. It also acts like a kind of 'notice-me-not' charm, helping you evade attention."
Once again, she cast the spell, speaking loud and clear this time, making sure that Harry was paying attention. The silence seemed to deepen. Harry thought he could now hear the blood rushing through his veins. It was a bit unsettling.
The girl now spent a few minutes teaching Harry both charms and exercising casting them, until she was satisfied with his performance. "I don't think Snape is right about you. You're much smarter and a quick learner, not at all the way he talks about you."
"You talk with Snape?" he wondered, allowing himself to skip the 'Professor,' just the way she did.
"Well, he's my head of house, and he speaks with the seventh-year almost daily."
"You're a Slytherin?" He wasn't sure how to feel about this.
"I am, but I assure you I'm built just the same as girls in the other houses." She didn't sound offended. If anything, he thought she sounded amused. "Now, I'm going to remove my own charms and let you cast. It's up to you to keep our privacy from now on."
As soon as she canceled her charms, Harry could hear the faint noises he had become so accustomed with, that he didn't normally pay them any attention, only now they seemed to be much louder. The girl waved her hand at him, beckoning him to cast his own charms. Harry complied. A moment later, the silence seemed to become even deeper. He noticed a fleeting appreciative look on her face, but she turned 'all business' as soon as he turned back to her.
"Before we can proceed, you need to learn one more spell, that is even more important in some ways. Girls learn this spell during first year, when the healer explains about the changes that their bodies are going through, yet boys should know it as well, just to be safe."
Harry looked a bit bewildered. She smiled and proceeded. "It's the contraceptive charm. A girl can get pregnant as early as age eleven, in some cases, but she should better wait until adulthood, if she wants to gain herself any kind of status and to assure the future of her children. Boys don't get pregnant, but most still wouldn't like to be burdened with children before reaching adulthood. It's their responsibility as well."
Harry nodded. He only had a vague idea about how things worked in this respect, and he was sure he would learn some more soon enough.
The girl explained the charm, the pronunciations and the wand movements and let him exercise each separately. She then demonstrated, casting it on herself. "The bluish fog that momentarily appears is the sign of correct casting. No fog or a different color means you cast it wrong. Now, you should cast it on me."
Harry followed the instructions, resulting in a much denser blue fog that took longer to dissipate. The girl seemed content, though. She sat on the only bed in that partition and beckoned him to her side.
"Tell me what you know about the differences between boys and girls, please, or actually – between men and women."
Harry blushed. He knew very little, really, never having learned anything in an orderly manner. "Well, men are usually taller and more powerful. Women have breasts, while men don't, and men have penises, but women have none." he blushed even redder as he talked.
"You look cute when you're so red," the girl teased him, making him turn even redder. "Don't worry. After we finish here it will be much less embarrassing and much more enjoyable."
She waited a moment for him to calm down before talking some more. "What women have instead of penis is a vagina – an opening between the legs that is used for the same purpose, namely for peeing and for sex. Have you ever seen one?"
Harry blushed again. "Not really. I saw some nude pictures in some magazines, but nothing more."
"Well, it's time you see a real woman naked." The girl stood up and opened her robe, letting it fall to the floor, revealing her body, hiding nothing. She turned around to let him get a good look from all directions. "Like what you see?"
Harry swallowed hard. The girl was quite big, about a head taller than him. As he was still sitting, her big breasts towered over his head, looking quite heavy, as they sagged a bit. He still liked them. As his eyes wandered lower, he noticed her flat tummy, with just a bit of swelling, as if keeping something inside and then a triangle of untrimmed hair, pointing at what looked like a fold between her thighs. He felt his body respond to the view, making him even more uncomfortable.
"I like it very much," he managed to say.
"Don't you think you should get naked now as well?" she asked teasingly.
Some instincts that he had never been aware of made him want to respond immediately. He then remembered the hand-me-down clothes he was wearing under the school robes and it dampened his enthusiasm. "Turn around, please," he said.
"Suddenly shy?" she teased again, yet turned around, letting him watch her trim behind while he quickly took off his clothes and wrapped them all with his robes, not to let her see them. He was surprised to find his penis stiffly erect. He hoped it wouldn't offend her, as he had no way to hide it.
"You may turn now," he said, once he made sure none of his regular clothes was visible.
She turned around, moving very sensuously, yet once she looked at him, she gasped. "You're way too thin for your age. Has anybody told you?"
He felt his cheeks heat again. "It's probably my built. I eat almost as much as Ron, but I stay slim."
She took another long look at him, her glance stopping momentarily at his erection. "Well, that's not what I'm here for anyway, but I think you should consult with a good healer about that." Her mood seemed to change subtly. "Now, before we proceed, I think you should learn a bit about our internals as well. Let's start with you."
She grabbed her wand and cast a spell that made his lower abdomen seem transparent. He could see his internal organs as if it was a scientific film, as he had once glimpsed at on the television, before Dudley changed to a different channel. It was fascinating, but somewhat creepy as well. Even his erect organ seemed to reveal its internal structure.
"As you can see, there are blood vessels that bring blood into this spongy area," she pointed at it with her wand, "and the muscles at the other side prevent it from going back, inflating the spongy area and making it almost as hard as a bone."
Despite the explanations, Harry didn't like seeing his body this way. The girl didn't seem to mind. "Now, as you can see, the tube that reaches to the end of your pin goes back, through this lump, whose name I just can't remember, splits into two sections that end at your testicles, where your sperm is produced. When the time is right, the sperm moves through these tubes and goes out of it, ready to do its job."
Harry nodded. He was relieved as she ended the spell, letting his body return to normal.
A.N. I know women use urethra for peeing, but as it comes out at the labia, that is the common point for it and the vagina, it seems acceptable as a first approximation. Further explanations would make the distinction clearer, although they are not part of this story, which is not a replacement for a real, scientifically correct, sex education text.