A bike that makes banana smoothies has been the star turn of Fairtrade Fortnight at Kemnay Primary. It's an ingenious bit of kit - as you pedal the bike, it powers a smoothie-maker on the back.
Everyone has had a go, including the school janitor and the headteacher, Anne Laing. Staff and students have pulverised hundreds of bananas into smoothies to sell at playtime at the Aberdeenshire school.
"The faster you pedal, the faster you make the smoothie," says nine-year-old Luca Fletcher, as he pulps another few bananas. "Can you please get off because I don't really want my fingers shredded?" one of the boys asks his friend, as he prepares to demonstrate how the wheels of the bike turn and activate the blender.
The bike is on loan from the Edinburgh Bicycle Co-operative and despite the youth of most of the cyclists here, so far no one has had to go home wearing a smoothie.
"They did want to try it without the lid, but we didn't," says P5 class teacher Rachel Hughes, who organised the event.
"You have to have your adrenaline pumping to make the blades move. If you don't move the pedals quick enough, the blades won't move," says another of her students, Kelvin Kidd. "The way we make them is we get two bananas, some ice and juice and we put it in the blender and somebody pedals it. And it makes a smoothie and we sell it for 30p."
But these are not just ordinary bananas, as the P5s tell anyone who'll listen: "They're Fairtrade bananas," Fergus Morgan says.
The class has been studying Fairtrade for its topic and pity help any parent who tries to sneak anything else into their trolley in the company of these persuasive P5s.
"Fair trade is when people are trying to be fair to other countries that don't have enough money and to the farmers who produce the food," young India Smith explains.
"They make sure they get the right amount of money, because sometimes they don't. They have not got enough money anyway, so it's not very nice for them and it helps make their homes better and it gives them the things that they need."
The school is hoping to achieve Fairtrade status. As well as raising #163;200 for charity this week, the topic fits in with class work on citizenship.
"They've had a visitor in from Traidcraft to assembly, to tell them about fairness in the world, and we had a tug of war to show them the differences between countries and what's fair and what's not," Miss Hughes says.
There are now more than 230 Fairtrade schools in Scotland, which became a Fairtrade Nation earlier this year, after all six cities and 18 of the 32 local authorities achieved Fairtrade status.
"Working towards and then becoming a Fairtrade school is great for the school and the local community," says Kate Jones, Fairtrade's education campaigns manager. "It puts the school at the heart of people's movement for change, enabling young people to develop new skills, knowledge and understanding.
"It offers teachers loads of ways to enhance the curriculum and it's fun and part of something happening all over the world. And of course it's great for farmers, who are feeling the support through earning a fairer price for their produce."
* To make a Kemnay Smoothie you need half a banana, half a cup of juice and two ice cubes.