Fourth to sixth year pupils at James Gillespie's will move after Christmas into the council's Darroch building half a mile away, for two years during construction of the new Gillespie's building in 2013.
Concerned parents told the council they wanted the move to happen after the summer holidays to allow pupils time to settle before prelim exams in January.
Advertisement
Hide AdAdvertisement
Hide AdLabour's education spokesman Paul Godzik said: "It is clear that a winter decant will impact on children and staff, and the HMIE report stated that all stakeholders believed that a decant half way through the academic year was 'not appropriate and detrimental to young people's learning'.
"The Lib Dem/SNP administration have again refused to put pupils and teachers first."