Harry looked at his students and thirty wide-eyed eleven-year-olds looked back. This would be the first time they'd seen the Defence Against the Dark Arts classroom with the desks and chairs stacks against the wall — the first time they'd seen it set up for a practical, rather than a theoretical, lesson.

"So far, you've been learning general theory," Harry said. "Today, we're going to start on the practical aspects of defending yourself against the Dark Arts. Protego is one of the most important spells you'll ever learn in your life. It, and its variations, have saved my life more times than I can count." The students stared at him with rapt attention. "Its strength, and its ability to repel hostile jinxes cast against you, is entirely dependent on how good you are at casting it. And, of course, no magical shield will do you any good if you don't get it cast in time."

Colin Aitkins raised his hand. "Yes, Aitkins?"

"Sir, what are the variations?" the boy asked.

"Good question. Does anyone know any of the other shield charms?"

After a moment, one of the girls from Ravenclaw said, "Protego Totalum. Mum uses it on the house."

Harry nodded. "Five points. You can use Protego Totalum to protect a place for a long period of time. Anyone else?" He paused, but no more hands went up. "There's also Protego Duo, which will protect you against physical attacks as well as magical ones, Protego Horribilis, which protects against certain kinds of Dark magic, and Protego Maxima, which is the strongest of them all. But for now, we're just going to work on good old simple Protego. Think about the person you want to protect, which will be you for now. Wands like this, move it like so, and Protego!"

"Protego!" they chorused, largely ineffectively. Here and there Harry could see faint traces of embryonic shields, quickly dissipating.

He moved throughout the classroom, correcting wand movements and pronunciation. Maybe this was a bit ambitious. I had trouble getting the hang of it when I first learnt it, and I was four years older than this lot are. "Wilkins, it's more of a forward movement than that. Rowland, you've nearly got it — concentrate as hard as you can on the idea of protecting yourself."

Just when Harry was about to accept that he would have to halt the lesson and admit frankly that he'd made a mistake in trying to teach them a spell more suited to fourth year students, a flicker of light caught his eye. Turning, he saw Michael Rowland fully surrounded by his magical shield. It was a weak one, already fading, but it was complete.

"Well done, Rowland! Give it another go."

The other students fell silent, turning to watch.

"Protego!" Rowland tried, and then again, "Protego!" The shield flickered into evidence again.

"What did you do?" Harry asked him.

Rowland stared at him. "The spell."

Harry grinned. "I know. I meant, what did you do that made it work, that time?"

"Oh." The young Ravenclaw frowned in thought. "I was imagining that someone was about to hex me."

"Anyone in particular?" Harry asked.

"My sister," Rowland said. He gave a wry grin. "She's really fond of the Jelly-Legs jinx."

"Rylla Rowland?" Harry asked, and the boy nodded. "Do you think you could have done it without thinking about that?"

"Not really," Rowland said. "Is that … is that wrong?"

"Not at all," Harry assured him. "It's just something I should have taken into account when I was planning my class." He turned to include the other students. "Right, hands up anyone who's never been jinxed or hexed or otherwise magically harassed." Only four hands went up. "You four, over here with me. The rest of you, keep practising, and do what Rowland did, imagine someone is about to cast something at you and you want to protect yourself from it."

Harry gathered the four students who'd never been the target of a spell together at the far end of the classroom.

"Are you going to hex us, sir?" one asked.

He gave them his best reassuring smile. "Now, what kind of teacher would I be if I went around attacking students? Am I right in thinking the four of you come from Muggle families?"

He got four nods in answer. Of course. Even without older siblings flinging Flying Bat Bogie hexes when they're in a temper, there wouldn't be a wizard or witch alive from a magical family who hadn't been on the receiving end of a Silencio or a Quietus at least by a frazzled parent.

"What have you done in charms so far?"

"Levitation," the girl who'd asked if Harry was going to hex them said. "And Dancing Feet."

"Dancing Feet it is, then," Harry said. "Pair up, face each other, wands out. And cast."

"Tarantallegra!" four voices chorused, and the next instant, four pairs of feet were dancing uncontrollably.

"Finite!" Harry said almost immediately, and freed them from the spell. "Right. Now you know what it's like to be attacked by magic. Off you go and —"

"That wasn't being attacked," the girl said. "That's just a charm!"

"A charm that the Death Eater Dolohov cast on Professor Longbottom in the middle of a duel," Harry said. "And he didn't do it for lack of other options, let me tell you. Any spell or charm can be used offensively, in the right circumstances. Professor Weasley once knocked out a troll with a timely Wingardium Leviosa, for example. So go work on your Protego, imagining that you're trying to stop someone casting Dancing Feet on you — and casting it where there isn't a teacher standing by to stop it straight away."

Chastened, the girl led the others back to join the group practising casting their shields. Harry was pleased to see that more than one of them had got the hang of it now, and those who were still struggling were producing stronger efforts than before.

He kept them at it for another half-an-hour before calling a halt, remembering how exhausting his own attempts to master it had been, at first. A wave of his wand brought the chairs and desks back from the side of the room and into neat rows.

"Take your seats," he said, and perched on the edge of his own desk as they did so. "Right. Now there's something I want to say to you all and it's really important. You all know that using offensive magic against other students is strictly forbidden at Hogwarts, but I know that there's always someone who thinks it's clever, and I also know that your instincts are going to be to try and deal with it yourselves. Get a bit of your own back." He folded his arms, thinking through what he needed to get across to them. "The problem with that is, then the other person wants to get their own back too. I knew someone —" Better not to say it was my dad and the not-quite-as-dead-as-we-thought Severus Snape. "— someone who was a student at this school who did exactly that, and it turned into a really serious feud that ended up with some people making very bad decisions." Thirty wide pairs of eyes stared at him solemnly. "Protego, and another spell I'm going to teach you later in the year, means you can protect yourselves — and other people — against anyone who thinks that Tickling Charms or Bat Bogey Hexes are a good idea. But the only place for you to use offensive spells or charms are in the classroom, or in the duelling club."

Thirty grave nods, although Harry had his doubts about how thoroughly the message had sunk in with some of them.

"If you're ever tempted," he said, "I want you to remember this class — remember, not just how to cast Protego, but also how it felt in that memory you used to feel like you needed to protect yourself. Making someone else feel like that, even if it's with a minor charm, is a bit cruel, and when you're cruel you open yourself up to worse things. Why is this class called Defence Against the Dark Arts?"

The sudden question threw them off balance, and it was a whole three seconds before Colin Aitkins raised his hand. Harry nodded, and the boy said, "Because it teaches us to protect ourselves from Dark magic and Dark creatures."

"And what makes them Dark?" Harry asked.

Rowland's hand went up. "They're evil," he said.

Harry grinned. "Well, yes, they are, but that's not what I'm getting at. What makes them evil?"

A different hand went up: Maisie Wilkins, who rarely talked in class but watched everything with calm interest. "You're trying to make us think that casting a Jelly-Legs Jinx on someone we don't like is the first step to becoming Voldemort. I don't think that's true, really."

"And you're an expert on old Tom Riddle, are you?" Harry asked.

Maisie flushed slightly. "No. But I'm an expert on me. I cast a Bat Bogey Hex on my brother in August, and I'm pretty sure I'm not significantly evil."

"Why did you hex him?" Harry asked.

"He had it coming," Maisie said flatly.

Harry had to suppress a smile. "But why did he have it coming?"

"He Transfigured my owl into penguin and wouldn't turn her back."

The entire class burst out laughing, and Harry let himself join them. "I suspect he did have it coming, at that," he said. "You were angry with him, when you cast the hex?" Maisie gave a single, decisive nod. "We all get angry, and when we're angry sometimes we do things we don't really mean. A lot of what you'll learn over the next seven years is about how not to use the skills and spells we teach just because you lose your temper at someone, because otherwise we'd have outbreaks of Jelly-Legs and Bat Bogeys every Christmas shopping season. But it would be different, I promise you, if you'd cast that hex on your brother because you really hated him, because you wanted him to suffer, to humiliate him — if you cast it in cold blood and not in the heat of anger — then you'd feel it. A part of you would start to grow a callus, and it's the most important part."

She frowned slightly. "A callus on my magic?"

Harry shook his head. "Your magic isn't the most important part of you. The most important part of you is your ability to feel for other people. To care when they're hurt, to worry when they're in danger, to want them to be happy. That's the part that Dark creatures don't have, and that Dark wizards have to kill off in themselves. And that's the part that you'll injure if you go down the path of returning hex for hex and jinx for jinx." He looked around the class, from one young attentive face to another. "So, does anyone want to have another go at the question? Why is this class called Defence Against the Dark Arts?"

Maisie slowly raised her hand again, and Harry nodded to her to speak. "Because it teaches us to defend against Dark magic, from others, and how not to use the Dark Arts ourselves."

"Five points to Hufflepuff," Harry said.

Colin Aitkin's hand went up. "Sir, have you ever used the Dark Arts?"

Harry nodded. "I have."

"But you're not a Dark wizard, are you?"

Harry grinned. "What do you think?"

"I bloody hope not," someone muttered.

"I think Professor McGonagall would be able to tell, and not hire you," Colin said.

You'd think. Harry thought back to the year his own D.A.D.A class had been literally taught by Voldemort. Best not to share that story. "I used two curses that would qualify as Dark during the war against Tom Riddle. One, I used in anger." He grinned at Maisie. "Not dissimilar to someone casting a Bat Bogey Hex on a brother who Transfigured their owl. And the other, I didn't do it to hurt someone, but because we were absolutely desperate and there wasn't time to do anything else."

"So what you mean to do matters?" Colin asked.

"What you mean to do always matters," Harry said. "What you actually do, those are consequences you'll have to live with, but with magic, what you mean to do makes a difference to you. Not so much for the person at the business end of your wand."

You alone know whether it will harm your soul to help an old man avoid pain and humiliation … green light flaring from the end of Severus Snape's wand and illuminating his face, set in lines of revulsion.

He shook his head slightly, dislodging the memory. "You've got seven years to learn all this stuff," he told the children. "For now, just remember — stay away from hexing and jinxing, even if it's really tempting. Because apart from the damage you risk to your soul, it'll earn you a twenty House point deduction and detention for two weeks. Class dismissed."

As the students filed out, Ron Weasley sauntered out of the D.A.D.A teacher's quarters and leaned on the balustrade of the balcony. "You're getting that 'do as I say, not as I do' thing down pat, I see."

"I'd rather none of them turn into Draco Malfoy," Harry said.

Ron jogged down the stairs. "It'd take more than casting a few Anteoculatia's to turn someone into Malfoy."

Harry shrugged. "Let them get good habits young, then." There was no way to really explain his bone-deep conviction that magic used in malice was inherently dangerous, however innocuous the spell, so he changed the subject. "Young Rowland's got promise."

"He's the one Ginny had to fetch off his broom," Ron said.

"We'd better do something to keep him busy, then." Harry hopped down from the desk. "If he starts finding the coursework too easy, there's no knowing what he'll get into."

Ron grinned. "Polyjuice Potion in Moaning Myrtle's bathroom? Casting unknown spells out of an old Potions textbook? Wandering around invisible at night and sneaking into the Restricted Section? Fighting basilisks single-handed?"

Harry rolled his eyes. "I was thinking more of an unwise Incendio setting fire to the Ravenclaw dormitories."

"Or us, given the D.A.D.A jinx," Ron said. "Crispy-fried teacher would fit the bill, wouldn't it?"

"You know, something occurs to me." Harry took off his glasses and polished them on the corner of his robe. "We'd really better break the bloody jinx before we reach Unforgivable Curses in the sixth year curriculum."

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A/N: Harry's memory is, of course, largely quoted from HBP.

In canon, of course, Harry & co learn about the Unforgivables in their fourth year, but then, they're being taught by a Death Eater, and Fake!Moody says that he's not supposed to be teaching the students about Unforgivable curses until their sixth year.

Thank you to all my readers, and everyone who has left a review. If you haven't, please consider it: this story has taken me more than 100 hours to write so far, so take ten seconds to give me some feedback!