It is Wednesday afternoon and I am seated in a darkened room between a hula dancer and a leather-clad biker - there are few respectable professions in which this is possible. I am at the world premi re of a play devised and now to be performed by 40 Year 2 children. They are all excited, I am a little anxious.

I know the children are about to lay down memories that will last a lifetime. Ask your female friends whether they ever played Mary in their school nativity. Some will answer “yes” with a pretence of modesty, others will spit out the name of the child selected ahead of them, others remain puzzled about why they were forced to be Joseph - few have forgotten.

There is a lot at stake as the curtain rises and “The Super Toy Blaster Bike” begins with a mayday call from toys on Planet Popadom where evil scientists are making toys bad. Toy soldiers launch a rescue mission only to discover that their plane is only a toy and will not take off.

The children show no sign of nerves. I look across at Tim, our head of drama, who teaches every child in the school. Music and dance are also taught by specialists. By Year 2, the children are comfortable on stage and it shows. Tim is loving it as much as they are. My anxiety subsides.

On stage Biker Barbie, Disco Barbie and Horsey Barbie are deep in conversation about their respective Kens. The phone rings. The toy sergeant explains with military precision: “Toys are being kidnapped. Our plane isn’t real. We need help.” Cue Mission: Impossible music and Barbies’

karate moves, like Emma Peel in The Avengers.

The play is now in full swing and the audience sways with mirth. The cast have no “error terror”. They improvise their way through wandering lines, help each other out and even ad lib for fun. One child throws himself to the floor with such unrehearsed vigour that Tim leaps forward, concerned.

They are in their element.

The engagement the children have had from creating the script is a big part of this. We have a gap year student, a former A-level student of ours, working with the drama teacher to transcribe their words and create a little ones’ Mike Leigh approach. This is really theirs, and you have to have a teacher who really knows what they are doing to make this work.

These children are able to be on stage - not without nerves, but it is not so daunting for them. Many adults couldn’t possibly get up and speak publicly, let alone feel comfortable, so this is a skill they get from drama.

A more subtle point is there is a lot of talk about teaching happiness and citizenship. Teaching these things through drama embodies them in children’s experience. This works much better with younger ones, for whom it is much better overall in terms of co-operation, listening, sharing, noticing and recognising all these basic qualities we are trying to instill.

We do a lot in terms of emotional development with circle time and so on, which works well with verbal children. Drama isn’t done in the same way - it’s a physical experience carried along by being involved, and you can really establish your own identity - that’s the area of interest for us.

We’re investing in children’s growth. If we overstress literacy and numeracy it can be at the cost of the underlying development of the child.

The play reaches its climax: the Kens storm the lab on Planet Popadom but the outcome is uncertain until Granny enters, rebukes the Kens for their aggression and handbags the scientists into submission. She extracts a moral: “That just goes to show that everyone should play with everyone else in the playground” before the Barbies and Kens fall into each others’ arms and the whole cast enters into an all-singing-all-dancing version of “I’m a Barbie girl”.

Then something extraordinary happens. At the front of the crowd, one child emerges, leading the dancing, singing her heart out, and others follow.

Bright and beautiful and strong she is, and yet this is one of our very quiet children. She writes stories of sad mermaids and lonely dragons and has been all but completely silent in drama so far.

We have not seen her like this before. Perhaps it is the tide of enthusiasm but she is wonderfully transformed.

I turn to look at Tim. His eyes are on her. He has seen the same thing.

This child has become more herself. She may never be quite the same again.

And that is what drama is for.

Kevin Jones is head of St John’s college school, an independent school in Cambridge