The Miracle Man, Tron Theatre, Glasgow

If there's a worthy criticism that can be laid at the door of this new play from Scottish playwright Douglas Maxwell, it's that it's too ambitious. At two and a half hours with interval, it spits themes out: growing up, growing old, mortality, social acceptance, faith, the politics of religion. There's a lot to think about, particularly for a work that's ostensibly aimed at young adults.

But then Maxwell's skill is to find a universal profundity in youth and its ending. So this six-handed presentation from the National Theatre of Scotland and directed by Vicky Featherstone is aimed at teenagers, but it's for everyone.

Here, the schoolchildren who aim to bring American hip-hop evangelist and fashionable chastity advocate the Miracle Man to their school cover their own insecurities with noise and bluster. Yet it's their PE teacher Ossian "Ozzy" MacDonald, manchild son of a famed Scots poet whose death from cancer is imminent, who carries much of the play's heart – quite literally, as we discover.

A picture of boyish optimism in his bright-red tracksuit, Ozzy's slumped shoulders suggest a man who is being slowly crushed by life. Keith Fleming plays the character to perfection, flitting between browbeaten despair and sweetly doomed optimism. The exchanges with his paranoid and overbearing boss, Mr Healy, engaged in his own private war with the technical department, are quick, closely observed and uproariously funny.

For all that this play attempts to sink itself into big subjects, it's unceasingly hilarious, particularly in the first half. Jimmy Chisholm's performance as Healy captures the manic spirit of Basil Fawlty and the profane invention of Malcolm Tucker. There are also some neat exchanges between Charlene Boyd's self-regarding Dawn and Shabana Bakhsh's shy but slowly emerging Fawziya, whose growing friendship is amusing – but not glib – in the way it reduces the divide between Christianity and Islam to the level of a playground debate.

So the play tries to do a lot and loses a little of its focus in the process, but no single exchange feels overplayed or unnecessary. It's got real heart in place of sentimentality, humour where it might have chosen to preach, and an affection for and understanding of its characters, whichever stage of life they're at.

Touring to 3 April ( nationaltheatrescotland.com )