It’s Saturday afternoon in York and shoppers have come to a standstill.

Well, not quite. There’s a lot of jiggling and wiggling, stamping of feet, hands in the air as “Big Ian” and his band Huge pelt their way through some Queen, Who and other rock standards.

“We might not look very pretty but we sound all right!” roars Ian from a stage rigged in front of Marks Spencer to appreciative hoots from a crowd which now stretches the length of Parliament Street, the city’s main shopping thoroughfare. Huge is holding one of its regular charity busks and the lure of retail therapy is no match for the band’s big sound - Ian’s richly resonating vocals complemented by soaring brass and irresistible rhythm.

Big Ian is no misnomer. He’s more than 6ft, large-framed, plenty of padding with a voice, character and gift of the gab to match. He has the afternoon throng in his hand, singing along and swaying on cue; he has been known to get thousands of shoppers sitting on the floor with just a lowering of his hands.

“Can’t believe I’m involved in this nonsense with an Ofsted next week!” he jests. More roars of approval. Obviously, being head of key stage 3 at Lowfield school, a York secondary, is perfect training for crowd control.

Teaching is Big Ian Donaghy’s other life, and when he’s not leading his band, he’s providing literacy and numeracy support to teenagers. Huge is legendary in the city. It has staged sell-out gigs at York’s Grand Opera House 11 times. When it played in front of York Minster for the switching on of the Christmas lights, 7,000 turned up. On that occasion Ian took one of his Year 11 pupils, Lisa Ward, with him to perform duets.

At the end of this Saturday’s busk, despite being pressed by admirers, he reacts quickly to a voice shouting, “Catch you later Sir!” Lee Parry, another Year 11 pupil, has come, at Ian’s bidding, to study the band’s musical technique. Ian draws Lee towards the stage, pointing to a guitarist. “Now you see how he tackled that bit, that’s what you’ve got to try and do,” he advises.

Bizarrely, Ian Donaghy, 35, believes that being a rock musician and a teacher provide balance in his life. “After a hard day’s work some people go to the gym, others get drunk. I like to raise the roof in front of thousands,” he says. Getting back to the kids on a Monday morning after a university ball, or supporting the likes of Liberty X, Atomic Kitten and Jools Holland, or playing a celebrity party (Bill Nighy and Tim Rice) is his form of de-stressing.

Ian Donaghy has gathered a posse of musicians around him, including three peripatetic music teachers - trombonist, sax and bass player - as well as Dave Kemp, a sax player who formerly played with Chris Rea, to perform cover numbers from jazz, blues, rock and reggae. “We do them very, very well,” says Ian. “We make them seem like they were our idea in the first place.”

A maths graduate, Ian initially took a job at Lowfield, a secondary in a poorer part of the city, working with children on the brink of exclusion.

When that contract came to an end he was retained by the school for numeracy and literacy support and as head of key stage 3.

He is at pains to point out that he is no Dewey Finn, the failed but charismatic rock star played by Jack Black in the film School of Rock. “I am not a performing clown. I am good at relating to pupils, but I am not the man they want to get sent to (for misbehaving). At school I am fair but firm.”

However, his other life proves a great icebreaker in his relationship with parents, especially when he has to make home visits. “I went to one home and the father welcomed me in saying, ‘Great evening at the Opera House the other night, Ian, come in a minute, I’m just waiting in for a suit from the school’. I said to him, ‘I am the suit from the school’.”

In fact, Ian Donaghy’s big black suits are a hallmark of his daytime persona. John Thompson, headteacher at Lowfield, says: “When he first came he spent time walking around with me getting to know the place and pupils thought I’d hired a personal bodyguard. He clearly has an affinity with difficult kids and those who need support. They don’t mess with him and they love the fact that he is a teacher who is also a very proficient musician.”

Ian Donaghy is a consummate businessman too. His latest wheeze has been to transfer his skills as motivational teacher and band leader to the boardroom, running a sort of Fame Academy for local businesses. He recently packed the opera house as people from 22 local firms came to watch colleagues perform after training from Ian. “It was an awesome evening, dealing with all the frailties of people not used to performing.” He now plans to promote the concept to businesses throughout Yorkshire and the North-east.

With the night job, not to mention family life (wife, toddler and another on the way) encroaching increasingly on sleep time - “it’s not the worklife balance but the awakesleep balance that’s the issue” - Ian Donaghy is adapting his teaching career. He has recently secured a part-time job as special needs teacher at the Mount, a girls’ independent school in York.

Diana Gant, the Mount’s headmistress, says there was never any doubt about who the job should go to. “He will make learning support the coolest thing on the timetable.”

www.hugepartyband.co.uk.We’re launching a new Friday forum on work-life balance next term. If you want to join the debate - with the chance of getting paid pound;25 - go to www.tes.co.ukworklife balance