"Five ... four ... three ... two ... one ... go!" We have lift off. A cheerful battalion of brightly coloured balloons rises in defiance of gravity to invade a sullen sky.
It reminds me of the children at playtime charging out on to the field; emerging en masse, expanding to fill the available space, getting smaller and more remote as they shrink into the distance.
Our playing field is a large one and covers the area where the old school was before they built the new one out of breeze blocks and leaky metal roof panels. And although most children know where the boundary fence lies, only a few go that far. They know its fine mesh is un-climbable - unless you happen to be gifted and talented in escapology like Harry H in Year 2 - and that what lies beyond isn't worth the effort.
On the other hand, a balloon's horizon might be limitless.
"It could go on forever, couldn't it, Mr Eddison?" says Alice. "It could take my dreams all the way to Africa ... Or at least to France ... Or even to Doncaster Prison, where my dad lives."
She flashes me an optimistic grin before going back to the more serious business of watching her dreams fade from view.
It's good to have a themed week where learning is not packaged into a number of separate freeze-dried containers to be given as per directions. The plan during our Hopes and Dreams Week is to write our heart's desire on a postcard, fasten it to a balloon, and set it free to find its destination.
There are a number of children on this tough council estate on the wrong side of Sheffield who have lived all their short lives without ever having played on a beach at the seaside, or clambered over boulders in the nearby Peak National Park, or even travelled on a bus to Doncaster. But why, for the sake of a balloon, should we let mundane facts such as these imprison them?
Of course, we need to achieve lift-off first. "It's a gas called helium. Because it's lighter than air it's perfect for filling balloons."
The children hang on to them as though they are skittish puppies. The two that got away earlier bob cheerfully against my classroom ceiling like Uncle Albert in Mary Poppins.
"Did you know there's a world shortage of helium?" says young Einstein. "I think we should have used hydrogen instead. It's lighter than helium. Hydrogen is the lightest gas in the universe. And it's the most common gas. And it's number one in the periodic table of elements. And-."
He needs to be interrupted. "And we can't fill our balloons with it because we don't have a canister of it and because it might explode when mixed with oxygen. Anyway, helium can be used to make Mr Eddison talk in a funny squeaky voice like this ..." God knows how many health and safety rules I would have broken if I'd actually breathed it in.
In a few minutes, the balloons have all but disappeared on a bitter north-easterly wind, the same one that is driving us back inside. The children take off their coats, launch them in the general direction of their coat pegs, and settle in front of the interactive whiteboard. On its screen a quotation rotates: "To those who can dream there is no such place as far away."
"My dream won't really get that far, will it?" says Alice.
"What, all the way to Africa?" I ask.
She rolls her eyes like I'm an idiot. "Naw, to Doncaster Prison."
Steve Eddison is a key stage 2 teacher in Sheffield.