Geoff Barton (pictured) is wrong to suggest that pupils cannot make progress in their learning during a single observation (“Credibility matters”, TES, 27 April). In 25-30 minutes, if the teaching is good, pupils should be able to show there was a point to their being in that class on that day. They will have learned something new or consolidated previous learning, and this will be clear to both the teacher and an inspector.

Mr Barton is right that a key part of Ofsted’s purpose is to help schools improve. Inspectors do this in various ways - for example, by highlighting strengths and weaknesses, and identifying areas for improvement. Inspectors also talk to teachers about what they have observed and work closely with heads and senior staff to involve them in the inspection process.

Inspectors are fully trained to carry out their tasks. Most were, and many still are, successful teachers and school leaders.

Susan Gregory, HMI and National Director for Education, Ofsted.