Chris is an intelligent chap who often has good, interesting and rational things to say.
However, why would the (sensible) policy to "sack bad teachers" somehow not work, Chris? What do you suggest - keep them on board? So it seems. That is dogmatic, anti "boss" union/"werkuz" pandering, m'fraid. It also ignores all the structural problems that are at the root of why Chris thinks it will not work. Chris' objections are just symptoms of other systemic problems in the State Education paene-monopoly. Fix the problems, not mitigate the symptoms.
You suggest they would get rid of curmudgeons, expensive older teachers and those not towing the line on test results. Your answer is to stay their hand when the proper solution is to sort out the obsession with tests, have vouchers, allow Heads to hire and set pay and make sure the Heads goals are rational and in the best interests of the school and pupils. If you do that, the Heads would not jeopardize their jobs by firing the valuable teachers, those educating their children and so attracting large numbers of parents wanting to slap down vouchers on their desks. Why would they fire experienced and skilled teachers if they set their pay levels THEMSELVES instead of having daft payscales imposed on time-serving union members? They would not.
Amazing how many problems can be solved by dealing with the fundamental dysfunctions that come with central control, aspects of union interference and State provision!