"We are going to build a bridge," the tall man in the hard hat tells the youngsters in the hall at St Fergus' Primary in Dundee - and immediately corrects himself. "No, you are going to build a bridge."
But this is no balsa wood model. "That is what I expected," says Gowriehill Primary teacher Fiona Kelly, who has brought her pupils to today's event, organised by Dundee Science Festival. "But just look at that. The pupils are impressed."
Almost 40-feet long, the cable-stayed steel structure the youngsters have assembled, with expert guidance from two members of the Institution of Civil Engineers, is indeed impressive. It's smaller than the Forth Road Bridge, but it looks similar and it fills the hall.
The imposing construction also supports the weight, swaying slightly, of the pupils as they walk across, followed by their teacher. "All bridges move in the wind and as they expand and contract with temperature," Michael Stewart reassures them. "If they were rigid, they would break."
Alastair Stewart, who delivered the introduction, explains the motivation for experienced engineers in working with schools. "Most young people have no idea what a civil engineer is. We are making them aware of possible careers in an enjoyable way. The Institution of Civil Engineers has a variety of workshops and resources like this that are free to schools."
A show of hands at the end of the session gives instant feedback on the workshop's impact. Three of the two dozen Primary 7s were considering engineering as a career, they say. Now there are six.
Dundee Science Festival's education programme organises primary schools and other venues to host events for a week. The benefits of easy access to these far outweigh the inconvenience of no hall for a week, says headteacher John Neeson. "It just means teachers have to be creative - but that's what Curriculum for Excellence is about".
On the drive to Newfields Primary, which is hosting two events today, Jennifer Young, Tayside manager for organisers TechFest-SetPoint, describes the festival as "two weeks of talks, comedy, family fun days and the schools programme - a week of activities aimed at Primary 4-7".
These are free to schools and funded by the education department, so all schools need to do is book places and organise transport.
The venues might be another primary school or one of Dundee's public spaces for science and culture, she says, such as Verdant Works, Discovery Point, the botanic garden or the science centre.
Outside Newfields Primary, two tall wind turbines belonging to a nearby factory turn gently in the breeze. Inside, half-a-dozen smaller ones are being assembled by Primary 7s, working in groups, to generate electricity that will light bulbs and sound buzzers.
How best to do this is the question. "That's no good," says Steven, as his colleagues stick blades in at random. "It's lop-sided." "It might work better with less blades," says Jamie, pulling a couple out.
Thought, discussion and trial and error soon get the job done. The bulb lights, the alarm buzzes and the youngsters look delighted.
Once wind turbines and solar cells have been investigated, the climax of the workshop is a race between model cars, fuelled by hydrogen from little electrolysis units. This creates hilarity, excitement and friendly banter about who won, since without drivers the cars shoot off in all directions.
There is also food for thought.
"Wind turbines are great ways of generating electricity," says Karen Ritchie, demonstration centre manager for the Hydrogen Office, who is running the workshop. "But what happens when there is no wind or sunshine? We need to store all this energy we are creating. One good way, as you have seen, is by using the electricity to make hydrogen, which can then be used to fuel cars."
Full-size hydrogen cars can be built now, she says, but until the Government seriously supports renewables there are two drawbacks. One is that garages offering hydrogen are scarce. The other is that the cars are pricey.
How much, Jamie asks, and she tells him. "A million pounds."
Laura Rennie comes into schools such as Newfields Primary with a collection of little friends that fly, swim, slither, crawl, run or wriggle, and half the fun of her sessions for the youngsters is wondering what will come out of her boxes next - and whether it will be cute, cuddly or frightening.
The other half is getting to hold and pet exotic creatures like a California kingsnake - wonderfully warm and smooth in his new skin - and a four-toed cinnamon hedgehog which, when set down, scurries along quickly.
"It's so cute," says Carly, P7. "I have learnt a lot today, even though I'm not keen on science. I have a dog and a hamster and I love all animals. I would like to take all these home with me."
Her friend Stevie feels the same way: "I've got three cats, two dogs and a hamster, and I go horse riding. I would like to study science at secondary school," she says.
But even for those less keen on scaly, furry and feathered friends, there is an obvious thrill in getting up close and personal. The youngsters are also learning a vital lesson, says the former Edinburgh Zoo outreach officer.
"I want them to go away knowing that animals are sentient beings with every right to life. Some kids maybe don't get a lot of love. But they can still learn to care for themselves and each other. Caring for animals and the environment is a great way to start."