They thought that when Glasgow City Council put up scaffolding to replace windows at Hollybrook Academy, Govanhill, the ext-erior could also be painted.
It would have been the first time it had been painted since being built in 1971.
But when a request to repaint the school while windows were being put in was sent by the school's parent council, they claim the council said "no".
Anne Marie Millar, whose 15-year-old daughter Roisin attends the 130-pupil school, said it had taken eight years to persuade council bosses to put the windows in. The former local councillor said: "We have been asking for years for new windows for the school because it is in a very bad state of repair externally.
"When we finally heard that we were to get the new windows we asked for a coat of paint too.
"It made sense to do it while the scaffolding was up as that would save paying for scaffolding twice.
"We were very surprised and very disappointed when the work finished and no painting had been done."
Council bosses said the £14,000 it would have cost to paint the school was out of its budget.
To put up the scaffolding again and paint the school will cost £21,000.
Anne Marie added: "If they had done two jobs at once it would have saved £7000 from the public purse."
Parents also claim that Hollybrook is the only secondary school in Glasgow not to have had an external upgrade.
Anne Marie said: "It would make such a difference to the young people to come into a smart, freshly painted school. It would really boost their morale."
Councillor Stephen Curran, executive member for education and young people, said: "I've met with the head teacher and the parent council to discuss their concerns and told them that Hollybrook is part of the city-wide school estate assessment to refurbish schools.
"We are committed to improving our schools and over £200,000 has been spent on replacing the windows at Hollybrook.
"Unfortunately, it is not straightforward to use the same scaffolding for a different purpose.
"Instead of saving money it would have cost more to do this."
Nicola Sturgeon, MSP for Southside Central, is backing the parents in their bid to have the school painted.
She said: "I think the position of Glasgow City Council is ridiculous.
"Hollybrook is a motivated school with great pupils, parents and teachers but the building has not been painted outside since the school opened.
"The money it would take to paint it is a relatively small amount and I do not understand the council's actions at all."