The books mainly focus on Harry, Ron, and Hermione (with occasional dalliances towards other students, primarily when they interact with the main trio). They don't really pair up much with anyone in the series. Hermione's daliance with Victor Krum isn't implied to be sexual, just romantic, and takes place largely off-screen. Harry doesn't pursue anything of the sort, due to Bigger Things Happening. Ron is largely unsuccessful in his romantic endeavors, due to his obliviousness.

That said, there's ample evidence that sex (or at least the preludes) occur at Hogwarts. As others have said, there's plenty of references to people kissing ('snogging') and similar 'PG' activities, which indicates that the awkward teenaged romances are occurring.

Moreover, in Book 4 (Goblet of Fire) during the big party there is a scene outside, where Harry observes two people (who I believe to be Moody and Snape) doing rounds of the ground. Snape blasts a set of bushes and is then seen deducting points from two students (whose names escape me), a boy and girl, who were clearly up to something.

There are lots of fantasy works where sex is totally ignored, just because it's something natural that has nothing to do with the main argument. The same way, authors usually don't explain you when their heroes go to the restroom and how much time they spend there.

The fact that HP novels are set on a college with lots of teenagers could seem like an excuse to introduce romance and sex into the story, however, the story is not about that. I think that JKR could perfectly added sex into its narration, but she knew that the effect would have converted its fantasy saga into something like Twilight, and she just didn't want that.

So... she did what any proud son of Great Britain would do when trying to avoid any matter, just act like it don't exist.

The building is not completely integrated. In Harry and the Order of the Phoenix chapter 17, Harry and Ron went to visit Hermione in the girls dormitory. In such a case the stair modifies into a slide, as the founders considered boys to be less trustworthy than girls.

There's no strong evidence either way, but statistics suggest someone is getting lucky

Since we obviously have no in-canon proof of students having actual intercourse, we have to refer based on what we can:

1. Wizard children aren't fundamentally different from Muggle children when it comes to hormones. They fall in love, they get jealous, etc., etc.




2. They have access to magical items like love potions which, if anything, makes it more likely that they're adolescents who might experiment




3. Considering the number of similarities between Real World Britain and Rowling's fictional world, the fact that teenage sex is hardly a rarity in Great Britain would suggest that such trends probably follow suit at Hogwart's.

However, we should also remember:

1. Students of wizardy aren't like typical students. Learning magic can be dangerous and Hogwart's can be a tightly controlled environment because of this fact (and other reasons, like Voldemort's growing influence).




2. Towards the end of the series / books, the overall tone and culture of the school is closer to that of one during wartime. The possibility of getting blown up can be a bit of a dampener on romantic outings.

It's all a guess, but it seems likely that a) yes, someone is getting lucky however b) it might not as common as we might guess.

Based on reality and hints in the book I believe there was sex happening at Hogwarts. When Ginny walks in on Percy snogging his girlfriend it seems like he is overly embarrassed to just be caught kissing. So I believe that while it wouldn't have been appropriate to actually talk about sex in her books based on readership she was alluding/hinting towards it.

Great point by Commusoft, The designers of Hogwarts at least expected the men to attempt to have sex with the women. Whether they were worried about it being forced or consensual is another matter...

If you've read the books, Harry bathes or washes two times in the entire saga, nobody pees, poos or farts, Harry is told to wash his hair the night before going to the ministry in The Order of the Phoenix. Maybe there's a spell or enchanted object that cleans you without bathing?

The sex part is a bit weird but you must not forget the Weasleys. It's just not what you want to graphically imagine Molly and Arthur Weasley having sex. It's not very sexy is it? But they do have seven children...

The rest of the wizarding world seems to be quite LOW on libido, for even after Hogwarts they only have one or two kids, even when they have the money...

I think if you're very busy and generally having fun, sex is the last thing on your mind, magic is just cooler than what we do at school, specially when we can't choose what we like and we have to deal with 10 if not more of school years compared to Hogwarts' 7. Not that it doesn't happen, I'm sure it does... but then what if they got pregnant? Where would they get condoms? If they are pure bloods where would they get muggle money to buy said condoms, is there a spell that makes girls not ovulate or boys sperm go puff?

And there is the fact that ALL rooms are shared, that puts a damper on masturbating right?

My question is how do witches deal with periods? Can they do "Evanesco" at home if they're muggle born ?

There are several hints and one real evidence that some students are really doing it, especially in senior years.

There are several long duration passionate kissing scenes in the canon. For example, when Harry took Cho on date, a guy who was rejected by Cho was kissing a girl such way. Ron and Lavender also used to kiss such way. Probability of having sex after such kissing is certainly not zero.

The real evidence is in Chapter 13 The Yule Ball of Harry Potter and the Goblet of Fire:

Harry looked around, back up the path, and saw Fleur Delacour and Roger Davies standing half-concealed in a rose bush nearby. He tapped Ron on the shoulder and jerked his head towards them, meaning that they could easily sneak off that way without being noticed (Fleur and Davies looked very busy to Harry) but Ron, eyes widening in horror at the sight of Fleur, shook his head vigorously, and pulled Harry deeper into the shadows behind the reindeer.

.....

.....

.....

'Ow dare you!' shrieked Madame Maxime. Her voice exploded through the peaceful night air like a foghorn; behind him, Harry heard Fleur and Roger fall out of their rose bush.

.....

.....

.....

'I'll explain inside,' said Ron quietly. 'C'mon...'
Fleur and Roger Davies had disappeared, probably into a more private clump of bushes. Harry and Ron returned to the Great Hall.

More in the same chapter:

Snape and Karkaroff came around the corner. Snape had his wand out, and was blasting rose bushes apart, his expression most ill-natured. Squeals issued from many of the bushes, and dark shapes emerged from them.

'Ten points from Hufflepuff, Fawcett!' Snape snarled, as a girl ran past him. 'And ten points from Ravenclaw, too, Stebbins!' as a boy went rushing after her.

Ofcourse, Rowling couldn't use more direct language to explain the intercourse in detail, but she gave solid evidences that they are doing it.

It was probably happening 'off-screen'.

Rowling has stated that she intended her characters to grow up, get hormones and have "sexual feelings". However, she didn't want to make the books overly coarse by including sex within the story itself.

The characters in Enid Blyton's Famous Five books act in a prepubescent way right through the series. In the Narnia books the children are never allowed to grow up, even though they are growing older.

I want Harry Potter and his friends to grow up as well as older, though I'll keep it all humorous, well within the tone of the books. I want them eventually to be truly 17 and discover girlfriends and boyfriends and have sexual feelings - nothing too gritty. Why not allow them to have those feelings?
_{(Sydney Morning Herald interview, 28th October 2001).}

It's a fair bet that sex was happening off-screen, but that Rowling didn't want to depict it. As such, we get the hints and suggestions that others have alluded to; for example:

Snape had his wand out, and was blasting rose bushes apart, his expression most ill-natured. Squeals issued from many of the bushes, and dark shapes emerged from them.

"Ten points from Hufflepuff, Fawcett!" Snape snarled, as a girl ran past him. "And ten points from Ravenclaw, too, Stebbins!" as a boy went rushing after her.
_{(Goblet of Fire, Chapter 23, The Yule Ball).}

This sort of slight of hand/innuendo also occurs in the movies - for instance when students seemingly recreate the car sex scene in Titanic in this deleted scene.

Rowling clearly thinks that her students have a sex drive. They have hormones and desires, in keeping with Rowling's intention to create rounded, realistic characters, not sterilized robots which remain children forever. As others have said suggested, the fact that the books were targeted at children meant that everything was kept in good taste and mostly left to the (older) readers' imaginations. That doesn't mean that sex wasn't happening at all.

There is no evidence there was sex or no sex. But one thing for sure is, if the Founders of Hogwarts does not want the kids to have sex, there will be enchantments in place to prevent that. such as the boys not being able to enter the girls dormitory.

It is unlikely that the kids were able to have sex in Hogwarts since enchantments in the walls could easily prevent this, if the founders frowned upon it. Why was Harry able to break so many rules? Most of his actions were normal just at the wrong time (in the dark of night).

They could get lucky at Hogsmeade though.