PP1: There is a lot of research out there that shows strict uniform policy generally boosts academic attainment, so there must be something to it
PP2: That's absolutely not true. There is a wealth of research that shows the opposite.
There is probably research on both sides of the scale (I haven't read anything about school uniform particularly). Usually when a stance is made for something, there will be 'evidence' refuting it on the other side of the coin: as is the case with most sociological/educational research (and there's a large overlap between the two).
IMO uniform is a fairly frivolous area of debate, but it's an exemplar of far more serious issues with the current UK education system. Such as 'quantity of time spent in classroom equals quality of education' (thanks for that, Gove). That's one example in which the opposite is demonstrably true, and the enforcement of that pointless law (parents grovelling for permission to headteachers for taking kids out of school for reasons that seem good to them) is enforced as some kind of 1984-esque money-making/social control scam. Win-win for the national/local governments there.
Another example is the ludicrous methods of literacy teaching all schools are now bound by; i.e. phonics. The Clackmananshire study had an extremely small sample, the subsequent Rose Report changed the entire system of teaching in this country, and the result (as evidenced from the first strategic release) was that the same demographic was being failed by this system of teaching as the last. Added to that is the complication that it's really affected kids' spelling and is bludgeoning to death the idea of actual enjoyment in reading. WTG, government!
And don't even get me started on SATS , GCSE and A' Level ...
What's really infuriating here is our education system being used as a political football and our kids being kicked from pillar to post in order to suit someone's ideological biases. In the meantime, the mantra RULES IZ RULES is shouted from the rooftops.
And yes, since this has happened standards have declined. I know this, as I see at first-hand exactly what comes out of the end of the pre-16 sector. And the quality of the degrees issued there are not what they once were, either.