The Teachers' Union of Ireland has raised concerns about elements of the new Junior Certificate programme, which is scheduled to begin on a phased basis next year.
First examinations are due to be held in 2017.
Speaking on RTÉ’s Morning Ireland, TUI Education Officer Bernie Judge said the union was not happy with the assessment model being proposed.
She said that the new syllabus will shift assessment from an externally monitored system to the school and teachers.
Ms Judge also said the union has had no discussion with the Department of Education about what resources will be available to help schools implement the new syllabus.
She said that additional teachers would be needed to support schools in implementing the syllabus and that improved technical expertise would also be needed.
Ms Judge said the TUI did not believe it would be possible to phase in the new system next autumn.
The new Junior Cert syllabus, which was announced by Minister for Education Ruairi Quinn, will see students rewarded for achievements outside the traditional classroom setting.
From next September, first year students will begin studying the new Junior Cert syllabus, with the emphasis for the first time on project work and practical learning, and not the final State exam three years later.