Our elder son was and still is more easily influenced than I think is good for him. In the local primary school he was not seen to do well although I am certain he is no less intelligent than the majority of the rest. Then we went to Africa and he went to a private English medium school - the contrast was stunning, his first report card dropped our jaws as we stood there anxiously, quickly scanning it while he mingled with his friends on last day. As a result we (a little but not very hesitatingly) sent him to a local private school once back in the UK. He did pretty well, as well as we hoped he would. His younger brother followed and did outstandingly well.
The difference was, in my view, very largely due to much higher levels of motivation among all the pupils, better upbringing - actually with a few different drawbacks (a few upstart, self indulgent spoilt brats with parents with "aspirations", one or two sadly lacking kids who were being given the best opportunity available (and why not, really)) but much less challenging in class. Overall I believe the atmosphere was healthier than too often in the state environment and, yes, probably to many eyes based on old values. The teachers were better and more motivated toward good results and they got them. Smaller class sizes undoubtedly helped. We worried about the stigma (inverted snobbery) even though this school never seemed to us to promote anything other than a reputation of good results (which they easily could justify). Educationally, we definitely made the right decision although we will never know how they would have fared in a state school.