The union has long championed smaller classes and acknowledged the focus on the infant years following recent research on early intervention strategies. Cuts in the size of primary 1 intake classes remain the union's top negotiating priority. But they are an integral part of a broad-based campaign on funding, as Mr MacBride, a learning support teacher at Govan High, points out.
"We are arguing that Scottish education should be appropriately resourced. We should be looking at the demands on teachers and education authorities and saying what does this mean in terms of staffing, accommodation and resources?" he said.
Mr MacBride stands by the Tennessee research project (below) which found that smaller classes in the infant years make a significant difference. "Clearly, large classes are harder for teachers to manage and organise and put more pressure and stress on teachers."
He believes the case for lower class sizes is unarguable. Schools are expected to do more for pupils than in the past and attend to individual pupils' learning, pastoral care and special educational needs, all of which place more burdens on teachers in larger classes. Despite the extra expectations, teachers have done well to raise attainment levels, Mr MacBride insisted.
"Pupil-teacher ratios in the United Kingdom tend to be worse and sometimes significantly worse than those in comparable European countries and pupil-teacher ratios have started to deteriorate," he said.
Ken Wimbor, the union's assistant secretary, recognises progress in cutting class sizes will be slow given funding levels over the past 10 years. "It will be staged and we are not looking to achieve it in one fell swoop," Mr Wimbor said.