The National Youth Theatre’s Rep company initiative aims to provide an intensive eight-month affordable alternative to three years of drama training, culminating in a 10-week West End residency. It’s welcome at a time when a lack of arts opportunities in schools, combined with high tuition fees, threaten to make acting a career out of reach for all without parental support.

Some of last year’s graduates have gone on to successful fledgling careers, but this year’s group are ill-served by this clumsy staging of Michael Morpurgo’s story about two teenage brothers, Tommo and Charlie Peaceful, who swap the beautiful rolling hills of Somerset for the battlefields of Flanders. Simon Reade’s crafty adaptation has already toured extensively as a one-man show, providing the intensity and clarity that this coming-of-age story of brotherly love requires as it exposes the horrors of war and a British Army policy in which those deemed deserters were executed by firing squads.

That clarity is badly muddied in an attempt to open the story up and provide roles for the entire ensemble. In an age when small casts are the norm, it should be a delight to have 15 people on stage, but too often the stagecraft is so poor it just looks as if an almighty pile-up has occurred.

The cast is so busy staging the first world war, it’s not surprising that they barely have time to concentrate on acting: performances are either too big or perfunctory and vocally monotonous; accents slip slide away; there is a crucial lack of detail and warmth, particularly in the brothers’ relationships. With more rehearsal some of this may yet be rectified, but in its current state the show fails to deliver the emotional punch of either the book or the one-man version, and sells both its young cast – and the many schoolchildren who will see this production – well short.

• Until 21 November. Box office: 08448 112334. Venue: Ambassadors theatre, London