While the two sides do not appear close to agreement, a spokesman for the Scottish Executive described claims that the Education Minister had reached a decision to reject future reductions as "simply untrue".
Ronnie Smith, EIS general secretary, also issued a statement making it clear the union was not proposing to hold a ballot in the autumn in pursuit of its aims.
Both the EIS and the executive said they would be examining the interim report of the ministerial working group on class sizes, staffing and resources. This makes no clear recommendations and serves more as a review of existing research and literature.
"Many researchers think that the evidence shows that a significant reduction in class size will improve pupil attainment, especially for children in the early years of schooling," it states. "Others suggest that such gains are prohibitively expensive and that alternative methods of raising attainment would be more cost-effective."
Questions remain over the impact of different teaching methodologies for different class sizes, and the impact of smaller classes sizes on behaviour, attendance and motivation.
"Although researchers disagree about the outcomes of class size reduction, there appears to be a consensus that reducing class size is expensive," the report states. "Some suggest that it is the most expensive educational policy option that can be chosen."
The report also refers to the Pisa (Programme for International Student Assessment) results, which show that, while Scotland has some of the largest class sizes, it still ranks near the top for maths and literacy.
Further research is being carried out by the ministerial working group. It includes an exploration of how Scottish authorities and schools make decisions on class sizes. A pilot study will also test a methodology for analysing the impact of class size on attainment in the fourth year of secondary education, using Scottish Qualifications Authority data.
Some commentators have suggested, however, that a proper longitudinal research study should be carried out, using control groups, to provide really robust evidence. However, this would be time-consuming and expensive.
Mr Smith said the EIS would examine the report at its next executive council meeting in September and look then at how to take forward its campaign. It wants an across the board reduction to a limit of 20.
"Modern teaching methods, which focus on individual attention and personalised learning, can only work with smaller classes," Mr Smith said.
"We must move on from outdated limits that were set over 30 years ago."
A spokesman for the executive said ministers were concentrating on delivering existing commitments to make significant class size reductions to 25 in P1 and 20 in S1-S2 maths and English.