In a frank interview with TES Cymru after the launch of his second annual report, Dr Bill Maxwell said schools need to raise standards, not wait for resources.
He added that some schools in deprived areas did perform well and that schools needed to do more to raise the achievement of poor pupils.
The report, launched at Coleg Llandrillo, Rhos-on-Sea, on Tuesday, says 84 per cent of lessons in primaries are rated good or better, as opposed to 60 per cent six years ago, but secondaries are stagnating.
Dr Phil Dixon, director of ATL Cymru, blamed scarce resources. "We need to refocus spending on those who need it most, and we need to accept - and act on - the fact that deprivation and exclusion affect the whole of society," he said.