In this "Think" Tank report they claim that students who are taught by poorly performing teachers lose 0.6 of a GCSE grade. This is the first time that the relationship between poor teaching has been quantified.
Now there are one or two problems with this report. Even without reading a sentence of it I can tell you that the conclusions are probably wrong. What they have done is confused correlation with causation. Just because you do some statistics and find a relationship this does not mean that one causes the other. A simple example is rich people own Mercedes. So if I buy a Mercedes then I will be rich - causation and correlation do not always follow. In this case how do you define a bad teacher? It should be someone who fails to teach the students, so that they do not learn and the only metric to assess this would be the metrics of learning - the exams. So actually this is a self-referential paradox!
Actually they use the figures relating the level of first degree performance in high performing nations as part of the measure of quality of teachers. Sorry but this is also ridiculous. I know many great academics who cannot teach. A great mind is rarely a great teacher. This assumes that teacher training actually counts for nothing and would invalidate their own findings that it should be extended.
Of course all of this could have nothing to do with the current problems for the Labour Government that used to have the mantra education, education, education and that is currently facing a teacher's strike. Given that IPPR is a Labour Party associated think-tank and that many use it as a training ground for political life.
Four more realistic causes of poor results are inadequate resources, inadequate social support for families, the number of people who are on lower incomes and a lack of parental input. These are things a socialist government might like to tackle, but after 10 years they have not managed to put the money into the real problems and have wasted it on surface fixes.