Interestingly, in this same week I came across this article from Channel 4 News about the suicide rate among teachers (it's almost doubled in recent years, with teachers now 30-40% more likely to commit suicide than others). The article draws a fairly clear connection between teacher suicide and the Ofsted regime:
In the past few years teachers have been held more accountable for students' achievements than ever before. Students making little to no effort; students with long-term personal or health problems; students working doggedly in very difficult circumstances. All assessed the same way - what the last school got out of them + x National Curriculum 'Levels' = their expected achievement. Unfortunately, people are neither machines nor products and it just doesn't work like that. Thankfully for us, some students will blossom in sixth form and 'outperform' based on the standards expected of them. Others will achieve exactly as expected and some will not. A Levels are still demanding academically, whatever you will read in the papers in a couple of weeks on results day. Hard-working students can do very well in GCSEs, but hard work alone will not get you to an A or A* grade at A Level (gratifyingly, nor will natural ability alone - both are needed for the top slots). Students' results depend on considerably more than just the ability, commitment and talent of their teachers (just as they should).
I don't know where Oliver Letwin obtained his knowledge of the recent workings of schools, colleges, prisons, hospitals and other publically-funded institutions, but I think he'd find it difficult to do much to increase the culture of discipline and fear.