Primary school teachers have warned that literacy and mathematical standards are at risk because of a lack of resources.
The Irish National Teachers' Organisation has claimed the revised curriculum - particularly in English - is too broad to be covered properly.
It also requires a lot of one-to-one teaching, which the INTO said isn't possible to provide in many classroom situations.
Deputy General Secretary Sheila Noonan said teachers can't do the curriculum justice.
"There was great enthusiasm for because it's very well crafted," she said.
"But teachers' success in implementing has proved less successful. It's challenging to do so in the context of very large class sizes and the absence of resources to do hands on learning that's demanded of the curriculum."