They sing about how they love being frogs, jumping, swimming and eating flies. They wiggle and stick their tongues out comically.

An inspiring display of froggery (or frogdom?) is nearly there from this group of 26 four and five-year-olds. It'll be perfect once they're in green leggings and T-shirts, and lit in such a way as to make them appear as though they've just emerged from a swamp.

In the meantime, an impromptu audition is called for to see which frog can lead the rest as they lollop across the road and treat their audience to The Frog Cross Code, a safe protocol to negotiate the highway.

By tomorrow, director Tim Yealland will no doubt have all of his frogs in a row as the children give two performances for friends and family – on a real stage at Leeds University – of The Great Northern Hippo,
a show the school has created with the help of a residency by Opera North over the last two years.

This is Little London Primary, a 189-pupil school in inner-city Leeds, which is surrounded by all of the problems usually associated with inner-city areas.

Head teacher Jill Wood says that, if the school had been given an Ofsted inspection at the time she took over three years ago, it would probably have been put into special measures. Everything, from educational attainment to self-esteem, discipline and morale, was poor.

Jill and her hard-working and dedicated team have turned things around, and in Little London Primary's most recent inspection it was judged to be satisfactory. It has moved from 243rd place (out of 243 in the city) to 180th, making it the most improved school in Leeds and 20th most improved school in the country.

Its involvement with Opera North was cited as a key factor in its new-found direction, performance, positivity and confidence. Walking into Little London Primary today, its atmosphere is certainly cheerful and workmanlike, even if a few of the 26 little frogs are falling out of line because it's almost lunchtime. Frogs' stomachs evidently rumble as loudly as humans do.

Their frogs feature in a 90-minute piece of musical theatre involving every child in the school, whose music and words were developed by the children with the help of composer Rachel Leach and Tim Yealland, who both work with schools across the country as well as professional companies like English Touring Opera.

Telling the story of how a young boy finds an ancient hippo bone, which is then stolen by an evil scientist and its DNA used to reconstruct a modern-day hippo, the show opens and closes with ambitious numbers composed by Rachel. Everything in between has been constructed by the children, from plotlines to songs. The story is loosely rooted in reality, in that a prehistoric hippo bone was found in Leeds and is now housed in one of its museums.

The only professional singer in the show is baritone Wyn Pencarreg, last seen with Opera North as Figaro in The Marriage of Figaro. He plays the evil scientist, and over the two years spent periodically visiting the school, he has noticed changes.

"Children who were very difficult to get involved in the project at the beginning, are now much more positive and seem to be taking pride in getting it right. They've all done fantastically.

"The satisfaction for me is in doing something that's unselfish. It's purely for the kids, and I take it as seriously as if I were in The Marriage of Figaro."

Tomorrow's performances of The Great Northern Hippo will represent a very special creative journey, then, one made possible largely because of Opera North's commitment to a role in the community that's about sharing the arts with everyone, taking the experience to those who might not otherwise become involved in music, acting or dance.

The children get to work with a professional director, composer, costume, design specialists and top-notch singers, who all commit to regular visits to the school.

This is not just an exercise in maximising future main stage audiences for what ON does at the Grand Theatre down the road, though. It's seen as a completely worthwhile activity on its own account – and one which, judging by the success here, is surely also worth replication across the country.

"Each class has constructed its own scenes and songs, and they've come up with great ideas about what they want with very little nudging from me," says Rachel Leach.

"When they've been a bit stuck about how they want the music to go for a song, I've started the process by suggesting bad ways to do it. They've then corrected me, and their own ideas have developed.

"One of the challenges for us is in negotiating the politics of each class, and then there are the obvious things to do with the age of children you're dealing with. We've only had four or five days a term here to work on the songs, although they do some work when we are not around. What's wonderful about this kind of
thing for us is the freshness of the ideas."

By May, the show had developed into book form, and in between all the usual business of any stressed school, including SATs and rehearsing the usual school play, intensive rehearsals for
Little London's first opera have gathered pace.

Every child who wanted one has a solo, says Tim Yealland, and in the case of Year 5, they all wanted their moment in the sun – which meant each one singing their own couple of lines.

Summer Godfrey, Danielle Edgar and Cameron Wigglesworth, all 10 and in Year 5, appear to have an appetite for more of the same after the shows are over this week.

"I've loved it because it's included so many activities," says Summer. "We've done acting, singing, dancing, making things from clay (the school has made all the props and costumes), and the story is funny."

Danielle says she found it "quite scary" when she first heard Wyn Pencarreg's baritone unleashed at full throttle. "I'd never heard anyone sing like that before, but he wasn't actually scary to work with."

Cameron says he enjoys playing the part of someone who everybody likes and finds funny. "Doing it has built my confidence. I'd like to do it again."

Head teacher Jill Wood says The Great Northern Hippo has been about the process rather than the end product – great though it appears to be.

"There are 33 languages spoken among children in the school, and there are seven faith groups. As staff we were increasingly concerned about children being able to access a meaningful curriculum.

"The process of whole-school involvement in creating something like opera is wonderful for building confidence and self-esteem because you don't have to have a certain reading or maths ability to do it and do it well.

"During the Little London Project, attendance at parents' evenings has gone from 13 per cent to 87 per cent, which is partly down to interest and a sense of community created by the project.

"The process has brought about all sorts of changes, including increased self-control among the children. It's helped to make the school a very special place to be. Having Opera North come here was like having jam on our bread, and we're not prepared to eat dry bread
any more."

The Great Northern Hippo was one of a group of initiatives in Little London by ON, including an Early Years group, whereby mums and pre-school children gather to make music and make friends and Echo Archive, which recorded the music, songs and speech of the local community.

On a city-wide scale, ON runs Opus, an out-of-school project for 11 to 18-year-olds to explore a wide range of art forms, and work with professionals to create their own work.

ON's next school opera project will be happening in Bridlington. But that doesn't mean Little London Primary will be left high and dry after the excitement of creating the Hippo.

"We'll be continuing our relationship with the school after this residency is over," says ON's director of education Rebecca Walsh. "The key to it all is sustainability. Projects like this raise long-term aspirations and self-esteem, creating an environment in which pupils engage with learning and culture and providing a vehicle for people to explore themselves.

"It's only right that as a publicly-funded organisation we share what we do in this way. And everyone from ON who has been involved would say that they have got a great deal out of it, too."