Expertise is important. But what sort of expertise

There is a really nice post over at Computing Ed on the issue of expertise in teaching. The issues are about (i) subject knowledge (ii) teaching knowledge and (iii) teaching knowledge in relation to how learners cope with your subject. Well worth reading and I like (as ever) Alan Kay’s  division of students into 1o:80:1o groupings. I am in general very sceptical about what students know.