When you see 100 children chanting Einstein’s theory of relativity you know it has to be opera, the kind that is very much the device of Scottish Opera For All.

Under the guidance of Jane Davidson, Sofa’s head of education for the past 21 years, the company has honed its work to a pattern of almost unchanging perfection. Sofa should set “If it aint broke, don’t fix it” to music and use it for its ring tone.

When Cole Porter was asked if he started with the words or the music, he used to say it started with a phone call. Sofa starts the same way, commissioning composers and writers to create a musical of topical or local interest to schools. This year composer Marion Christie and writer Ross Stenhouse have come up with The Big Bang Show. Although the origin of the universe gets a mention, it is really an essay on energy and the environment, but it was too good a title to discard.

If the children of Scotland but knew it, Stenhouse is their favourite playwright, having for years written for the popular Hopscotch company before the offer to work with Sofa gave him the chance to explore his talent for lyric writing.

I doubt whether he knows the meaning of “dumbing down”. For Hopscotch, his historical romps had enough material for junior honours, and his libretto in this show tells all you need to know about the world energy problem in the cheeriest of rhymes.

Christie’s task, which she does extremely well, is to write music that will attract, challenge but not defeat children, given that they must learn it within weeks, possibly in a school not blessed with a musical specialist, such as St Ignatius’ Primary in Wishaw, North Lanarkshire.

As is standard, the school had received the pack of songs, lyric sheets and the vocals CD, as well as the collateral teaching aids, two months before show time. A fortnight before the big day, Sofa send a musician to check that the homework has been done. Then the hit squad of musicians and singing and drama animateurs arrives for a day of costuming, rehearsal and performance.

The P5-P7 teachers watch with interest as the quartet set about transforming their 100 children into an opera company. Coaching and coaxing the stage work is mostly drama animateur Abbie Wallace’s job, and she constantly models every step and gesture.

Once the songs and action of the groups of fission chips, combustible energy and environmentalists have been worked through, the moment comes when the costumes are handed out. This is always a time of excitement and wisely Sofa allows lunchtime for passions to cool. Then, in the afternoon, there is the dress rehearsal and half-hour performance.

Dressed in a mask and mummer’s gown of purple, indigo and mauve, but still modelling the action for everybody, Wallace sings the role of Gaia, alongside her two vocal animateurs. Stephen Faughey, in a top hat, frock coat and whiskers, plays Lord Kelvin and Alan McKenzie, with a mop-headed wig, is Professor (“That is the truth about nuclear fission. Trust me, I’m a mathematician”) Einstein.

Make no bones about it, these people are genuine singers. So it seemed reasonable to wonder what they are doing cramming into a minibus with the latest props every morning and driving off to some primary school, unloading all the gear and spending four hours persuading over-excited children to obey the rules of theatre, singing a bit, and then packing up to drive somewhere else the next day.

“I think it’s brilliant,” says McKenzie. “I just love the instant reaction from the kids.

“You get to know them; they call you by your first name. We have a lot of fun and they love to see us acting with them.

“I work for a spell with Sofa and then go off for a while and do something different. I do West End shows, had a run with The Phantom of the Opera, sang with D’Oyley Carte and West Australia Opera I But it’s good to come back. It’s hard work but I like it.”

The children like it too and their acting headteacher, Michelle O’Halloran, thinks it is “Fantastic! Fabulous! Well worth the money!”, sentiments which are likely to be echoed as Sofa continues its fully-booked, three term programme this session. The tour is not quite an opera a day, as the visit to Tiree needs one day for the travel, but otherwise an average of 100 children in 120 schools from Ayr to Cromarty are singing out the stark environmental message: “It’s time to make your mind up; this isn’t a wind-up.”

Scottish Opera, tel 0141 248 4567www.scottishopera.org.ukThe 5-14 curriculum support pack, music preparation session and workshop costs pound;670