'Too many temps'
David Eaglesham, general secretary, said young people were entitled to continuity of education and many parents did not know how many teachers appeared before their children.
A recent report from the European Trade Union Committee for Education examined temporary contracts in over 20 countries. Only England reported levels of temporary teachers greater than in Scotland.
Mr Eaglesham also criticised West Dunbartonshire for using teachers qualified in other subjects to plug gaps instead of filling posts with a trained specialist.