The Festival of British Youth Orchestras opened its three-week run in Edinburgh and Glasgow this year with a clutch of concerts by visiting orchestras from Switzerland, Germany Canada, the Nordic countries and Ireland.

The highlight of its last weekend was the premi re of Orkney-based Peter Maxwell Davies’s High on the Slopes of Mount Terror, inspired by Antarctica and performed by Chetham’s Symphony Orchestra from his home city of Manchester.

Although these concerts demonstrated the ambition and high standards at the upper level of youth music, the middle week revealed the more everyday stratum of classical music in British schools. The standard varied from very good - as exemplified by the Edinburgh Schools Wind Ensemble and the Junior Academy Orchestra from Glasgow’s Royal Scottish Academy of Music and Drama (RSAMD) - to barely acceptable.

The Durham County Youth Chamber Orchestra fared particularly badly having faced a series of problems, including the last-minute replacement of their conductor through illness. Nonetheless, its ragged performance at Central Hall in Edinburgh undermined a potentially absorbing programme and raised a vexed question for the festival.

While there is great value for the youngsters in participating, the festival is a public event. It is therefore duty-bound to try to ensure acceptable standards. What can be taken with an indulgent smile in a school concert is not good enough in this setting.

Durham was not the only ensemble to fall below par. Malden Young Strings lacked the necessary technical and musical consistency, although its age range was the most varied of the groups I heard, which may have been a mitigating factor.

The problem for the festival is knowing in advance precisely what any given orchestra will sound like. A group which can boast fine players one year may struggle the next, and young musicians are perhaps more likely than most to have an off-night.

Happily, the vast majority of orchestras taking part more than justify their inclusion, although most will suffer wobbles in the course of a performance. This happened to the East Dunbartonshire Secondary Schools Orchestra, which in its Edinburgh concert alternated from very good to rather untidy in an unpredictable and rather over-anxious fashion.

Two of the best performances, from the RSAMD Junior Academy Orchestra in Edinburgh and the West of Scotland Schools Orchestra in Glasgow, were conducted by professional musicians rather than teachers. James Durrant and William Conway drew excellent playing from their charges. It may be that a professional on the podium spurs the players to greater efforts, if only because the conductor may demand more from them.

The Edinburgh Schools Wind Ensemble, however, under its teacher Stephen Callaghan, also illustrated two of the great strengths of youth orchestras. It would be difficult, if not impossible, to organise and run a full-size orchestra dedicated to wind and brass instruments in the commercial world, but they were able to programme imaginative and unusual music such as Martin Ellerby’s Dona Nobis Pacem without too much concern about harsh box office realities.

That freedom of programming was evident in many of the concerts and provided some demanding tests for the players. While the West of Scotland Schools Orchestra focused on a relatively conventional programme, culminating in a major work (Mussorgsky’s Pictures at an Exhibition), the Shropshire Youth Orchestra played a dozen shorter pieces, a strategy which ensured variety but left me wondering how they would cope with a more extended symphonic work.

Overall, the report card should acknowledge several signal successes and some could-do-betters. While there is far more to youth groups than concerts, the festival has to be a showcase for achievement.