The head of 600-pupil Argoed comprehensive, in Flintshire, says that it is impossible for her small staff to avoid all 20 tasks proscribed by the agreement.
Like all schools in Wales, she has only had pound;3,500 to implement the deal. "Funding is limited," she said. "We need a good input of cash. We only have one support worker, who now does admin work one day a week. Our learning support assistants are covering teachers as well, even though it's not in their job description."
Argoed's art and music departments each have only one teacher and no technical support, so staff still have to prepare their own materials, regardless of what the agreement says. Many teachers have volunteered to put up their own classroom displays.
Mrs Brown has forwarded union information about the agreement to teachers, and has held meetings with staff where they agree to share out the limited support available.
She said: "Different people need support at different times of year, for example if there is a drama production or sports day. Because we're a small school, we all roll up our sleeves and help each other."
Tim Clisby, senior geography teacher at the school, said: "My department could do with an admin assistant for half a day a week, organising cupboards and doing things that don't get done otherwise. "But teachers are great make-do-and-menders. If we refused to put up displays, the school would be a poorer place for it."
Mrs Brown said the deal had not helped existing problems. Welsh-language lessons have been compulsory up to age 16 since devolution in 1999, but Argoed has difficulty recruiting Welsh-speaking teachers.
She said: "Teachers are knocked all the time. So the workload agreement hasn't made the job more attractive.It doesn't make things easier for me at all."