School unions allege the Ministry of Education deliberately withheld its latest roll-growth estimates so they could not be used to undermine the Government in the debate over class sizes.
Figures dating from August last year were only published recently.
They show the ministry expects the number of school children to reach an all-time high of more than 800,000 by 2024.
That will require more teachers or more crowded classrooms.
Teacher unions say the figures were compiled more than ten months ago, but held back so they could not be used in the recent debate over school staffing ratios and class sizes.
Angela Roberts, vice-president of the Post Primary Teachers Association (PPTA) says the ministry should have published its new roll-growth estimates during the debate over class sizes.
