Could you work out how to tell whether a teacher is productive? Which bits of the improve,ent in performance of pupils can be assigned to which teachers? If a child I teach English starts to score more highly 8n their history essay papers, is that my productivity or his/her history teacher’s? If someone with behaviour issues starts to do better and behave better, is that result of my strong teaching, or their form tutor doing some pastoral work, or a mental health professional, or their parents laying down the law?
They aren’t widgets in a machine. Any improvement is a product of ream work.
Though you may be unaware that, even so, teachers’ pay has had an element of payment by results for quite a while now (UPSand progression up the scale are based on targets around pupil attainment).