This paper is based on a series of previous research studies looking at the impact and development of teachers in the UK and internationally. It suggests that there is no convincing evidence, in terms of test outcomes, that some teachers are more or less effective with equivalent pupils. This is not necessarily because teachers are not differentially effective, but because the calculations involved are not possible with our current methods. And, of course, this is not to suggest that teachers in general do not make a difference--only that they are not obviously differentially effective. However, there is indicative evidence, particularly from pupil reports, that there is considerable variation in the skills, even very basic skills, of teachers. This may be partly the result of variability in the process of admitting and qualifying trainee teachers. There is also good evidence that the quality of pupil-teacher interaction in schools is linked to pupils' sense of justice, trust in others, and reports of citizenship activity. Perhaps then this is the clearest difference that individual teachers make, on the wider outcomes of schooling. It may also turn out to be one of the most important. (Contains 1 note.)