Graham Donaldson, deputy senior chief inspector, told an early intervention meeting in North Lanarkshire on Wednesday that a significant proportion of recently inspected classes had more than three attainment groups. More time was spent on interruptions and managing than teaching reading.
But inspectors had found four schools in disadvantaged areas achieving reading standards well above national attainment targets.
"These schools provide convincing evidence of what can be achieved with high expectations, effective teaching and a whole school approach to reading. " Mr Donaldson said.