My name is Just," the woman in the striped T-shirt and matching socks says. "Well, my name's actually Justina, but all my friends call me Just, so you can call me Just, too."
She has the exuberant manner of a children's TV presenter, all bouncy curls and bouncier enthusiasm. "Let's talk about brilliant feelings," she says. Then: "Feelings come from our brilliant brains. Can you think of any more amazing things that come from inside our brilliant bodies? Because our bodies are brilliant, aren't they?"
At this point, she pulls back a curtain in the corner of the room. Behind it is a female head on a plastic torso. "This is Tam," says Just. "She's a bit like a big doll, but she has see-through skin."
Indeed, where there should be skin, Tam's torso reveals ribs, lungs and a cross-section of intestines. "Make a loose fist with your hand," Just says. "That's about the size of your heart. Now" - here she invites a small boy to come to the front - "point where you think Tam's heart is." Gingerly, the boy taps the centre of her ribs and the area immediately lights up phosphorescent red. In a very literal sense, Tam has a brilliant body.
In the narrow mobile classroom, the rest of Wilberforce primary's Year 2 watches wide-eyed. Outside, the walls of their west London playground are adorned with colourful murals; inside there is only grey fabric, covering the floor, the walls, the ceiling. Here, in the grey dark, they are learning to talk about their feelings.
The Life Education programme, delivered by children's charity Coram, currently runs in 4,000 primary schools across the country. The aim is to provide lessons in personal, social and health education topics, such as self-esteem, healthy living and positive friendships. Coram's PSHE lessons, however, are not conducted by red-faced teachers but in significant part by Harold, a socially awkward puppet giraffe, and by Tam, the luminous mannequin.
"Children love puppets," says Emma Rogers, Wilberforce Year 2 teacher. "Even though they know it's not real, it makes it easier to talk about emotions if they're talking to a puppet. The whole experience just captures their attention."
The pupils suitably absorbed, Just introduces them to Tam's intestines ("this part of the body has a long name, beginning with `int', and it's not `internet'"), which light up in luminescent orange, resembling cut- price baked beans. "This part of the body will help us break our food down into - what do food and drink and oxygen all give in the body together?"
Several children put up their hands. "Running!" one says.
"Yes, you need it to go running," she says.
"Bones," another pupil volunteers.
"Yes, good, you need it for your bones," Just replies. She pauses. "Has anyone heard of energy?"
This approach - never to negate, never to contradict, always to focus on the positive - is a deliberate technique, taught to all Coram educators. In her life outside the grey fabric walls of the classroom, Just is Justina Horne, training manager for Coram Life Education. "Because the children are with us for such a short time, you don't want any lull in their positivity," she says. "You want them to feel valued. If I answer a question with `well done, but.', that `but' negates the `well done'. You work extremely hard, right from the start, to make the children feel special."
Energy, Just continues - "en.er.gee!" the children repeat - is what helps them to sit up straight, to put their hands up, to answer questions. And, she adds, it is what enables them to have feelings.
This is where Harold the giraffe comes in. Harold is having strong feelings right now. "Harold has been so excited all morning," says Just. "He's been saying, `Where are Year 2?'" Now, however, his excitement has turned to nervousness. "Harold can be shy," she says. "That's a feeling, too, isn't it? Sometimes when you see a group of new people, that makes you shy. Harold? Hello?" She struggles to open a cupboard door. "Harold's just getting ready - I can hear him," she says. She digs her fingernails under the edge of the door - "he's very shy" - and, finally, it snaps open and Harold emerges: a giraffe neck and head, fitting neatly over Ms Horne's arm. "Oh!" the children breathe.
Harold, along with his friends Derek the penguin and Kiki the kangaroo, have been designed by the award-winning children's BBC puppeteers responsible for Hacker and Dodge, the canine duo who have inherited the continuity mantle once worn by Gordon the Gopher. Coram is one of 10 charities the BBC has chosen to work with, offering practical help and general expertise.
Harold, already used by Coram educators before the BBC partnership, has been given an extensive giraffe makeover, gaining a coterie of friends in the process.
"Harold and Tam - they're my colleagues," Ms Horne says. "For me, as a 40- year-old woman, to be asking children's advice would be a bit strange. But a puppet can. Then children can take on the mantle of the expert and share their expertise.
"But it's a bit of a bizarre job. You try going to a pharmacy and asking for a support bandage for a giraffe-induced injury."
Now fully out of his cupboard, Harold is jiggling with excitement at seeing the pupils. He is about to host a party, it transpires, and is therefore a veritable melodrama of intense emotions. "How's Harold feeling about the party, do you think?" Just asks the children.
Seven-year-old Jade Thomas-Emeh thinks about this carefully. "Harold is very different from me and my friends," she says. "He's a giraffe, and we're not. But I think we all have the same feelings. Giraffes can have feelings, even though they're different."
Containing his various emotions, Harold retreats into his cupboard to focus on last-minute preparations. In his place, Sam emerges: a small boy puppet, with Muppet-like flip-top head. Sam is upset, because he is unlikely to make it to Harold's party: he has a headache. But - and here Just holds up a bottle of medicine - he has found a potential solution. "Should I take it?" he whispers in her ear. She relays the question to the class, and together they look for an answer.
"It says `cough medicine' on it," Just says. "But you don't have a cough, Sam. And it has your friend's name on it." Then, to the pupils: "He says his friend left it here. What would happen to Sam if he takes someone else's medicine?"
A boy puts up his hand. "You'd get germs."
"Yes," says Just, again all boundless positivity. "If you drink from the bottle, and someone else did, you could get germs. Usually you use a spoon, don't you?"
Once it has been established that Sam should avoid his friend's medicine and instead lie down before the party, attention reverts to Harold. Just switches on the classroom TV and Harold appears in a party hat, adjusting collections of snacks on paper plates.
This is one of four educational films, produced in association with BBC volunteers. Pupils ranging from Years 1 to 4 each have their own films: Year 1's video looks at healthy living and friendship; Year 2's examines feelings and being left out. Year 3 pupils discuss conflict resolution, while Year 4 talk about choices they make with their friends.
"Friendship is so important to children of that age," says Ms Horne. "Even something like being left out at a party can keep them awake at night."
This, in fact, is the issue being dealt with in Year 2's video. Derek, a bafflingly officious penguin, has decided that only partygoers wearing costumes can dance at Harold's disco. Kiki the kangaroo is not wearing a costume, but she likes discos. Derek, however, informs her unequivocally that she will not be allowed to dance: "You'd spoil all the photos," he says. "You can't join in. That's the rule".
Just pauses the video. "How does it feel if other people are leaving you out?" she says. "It's not just the things we do that can change our feelings. Other people can do things to change the way we are feeling, too. Wow. That's quite powerful."
"The party looked fun," asserts seven-year-old Belin Munshi, his words measured. "But Derek was rude. If he was my friend, it would make me sad if he talked to me like that. I don't know what I'd do."
This is precisely the predicament Ms Horne hopes to resolve. "Think of some people you could talk to if you're feeling sad or worried about something," she says. "Who would you talk to? Mum? Dad?"
"The giraffe," one child volunteers.
"Brilliant!" she says. "Talk to a friend."
A phone in the corner rings and Just picks it up: Kiki has decided to talk about her problems with her friends at Coram Life Education. Just listens attentively, offering the occasional "mm-hmm". Then: "Go and tell Derek and Harold how you feel, because they're usually your friends, aren't they?"
She hangs up, and starts the video again. Kiki is now talking about her feelings with Derek and Harold. "I'm sorry I said you couldn't dance at the party, Kiki," Derek says. "Do you forgive me?" As an apology, it is slightly indifferent. But the children are content. "I'd like to go to a party like that," says Jade. "It looks fun."
Such reactions, however, are not universal. "One of the great things about this job are the different responses you get from different classes," Ms Horne says. "This group weren't exactly hurling abuse at Derek. But last week, I had a class who said that Kiki shouldn't be friends with him. It depends on what kinds of experiences they've had."
But the underlying message is the same, regardless. "It lets them know that it's OK to talk about their feelings," says Ms Rogers. "Once they realise there's an adult or a friend to help, they will always turn to someone." She has noticed repeatedly a significant rise in the number of pupils asking for emotional guidance in the months after the Life Education session.
The intention is that they will go on to apply these rules throughout - and beyond - their school years. "If we thought what we were doing would only last for this hour, or this week, or this year, we would feel that we weren't doing our jobs," says Ms Horne. "We want children to be able to make conscious decisions about what's best for them, to weigh up their choices. It's about educating these children through their lives."
She turns back to the pupils. "It's time for lunch, isn't it? It's time for you to go and get a bit more. " She pauses, expectant, and the children pick up on their cue. "En.er.gee!"