Jim Thewliss, general secretary of School Leaders Scotland, said the squeezing of budgets is "now starting to bite" in schools and classrooms.
In a grim assessment, he said staff wanted to promote aspiration in pupils but are now in the position of "managing expectations".
Mr Thewliss made the comments following the publication of the draft Scottish Budget on Thursday. Deputy First Minister John Swinney, the acting Finance Secretary, admitted he had set out “a pretty bleak picture” to MSPs as he published the tax and spending plans.
Cosla, the council body, had asked for £1 billion to address multiple challenges, but said the cash allocated for 2023/24 amounts to an uplift of just £71 million once policy commitments are taken into account.
Speaking on the BBC's Sunday Show, Mr Thewliss said: "There have been year-on-year cuts within the education budget over the past, certainly 10 years, perhaps even longer than that.
