It is a relief to see someone of Dylan Wiliam’s stature questioning the 30-minute lesson observation policy adopted by Ofsted (“Teaching expert challenges Ofsted to prove its ‘integrity’”, 3 February).

Progress has quite rightly become a major focus, but observing lessons for only 30 minutes is putting enormous pressure on teachers to demonstrate learning progress in every lesson. Good teachers use some lessons simply to engage and motivate learners, to initiate debate, to stimulate curiosity or to pose a problem. Deeper study and progress will follow in subsequent lessons.

“Teaching by numbers” and straitjackets should have no place in our schools and colleges, and yet this is exactly what is happening under a system that tries to judge the effectiveness of teachers by watching them once for 30 minutes.

Robert Powell, Educational consultant and former headteacher, Stafford.