OK, I guess many people won't agree with this post, but so be it. I believe that school uniform is wrong - always have done, and still do (and it's now a very long time since I was in school!). I know that's an unpopular opinion, but it's the one I have, and here's why.
School uniform is essentially all about conformity and authority. It is about making sure that everybody looks the same and does as they are told. Now, of course, I don't want to see kids run riot in schools, but I believe that 'discipline' in schools should be based on an encouragement of mutual respect, not on petty authoritarianism. Indeed, I've seen that kind of idea work very well in the primary school my children went to, which had a very open plan layout - the kids were mostly pretty well behaved, because they quickly learned that any disruption or noise was actually disturbing to many other people (including their friends and siblings) who were trying to do things in neighbouring areas. They didn't like having their activities being disrupted, so they learned not to disrupt others. A simple lesson, and a far better one than the simple 'fear your masters, and do as you are told' kind of stuff (I'll come back to that idea).
The argument that always gets thrown up in any discussion on this subject is the 'but what about poor people who can't afford new clothes and might get bullied for not wearing the right thing'? My answer to that is quite simple - shouldn't we be teaching kids that it's not OK to bully or mistreat someone because they don't 'conform'? Shouldn't the lesson by one of treating people with equal respect, whatever clothes they are wearing? Surely that is a more useful lesson for children to learn than 'conform or else'? In my opinion we would be better allowing them to express themselves and their own identities, while teaching them that everyone should be equally respected regardless of those 'identities' (chosen or otherwise). Let's deal with the problem of bullying and discrimination by dealing with those who are doing it and teaching them that it is wrong, rather than by actively encouraging such ideas through enforced conformity. We should foster and encourage diversity, not suppress it and send a message that it is somehow a 'bad' thing - the potential implications of that should be fairly obvious.
Obviously, there is an argument for providing some poorer families with extra help to ensure their children have some reasonable clothes to go to school in, but then in my experience many school uniforms are not exactly cheap anyway. Increasingly so, in fact. When I was in school, I had to have an official school tie, but that was it (apart from sports kit and the like) - it was black trousers, black shoes, white shirt, royal blue jumper, etc., but those could be bought from anywhere. That same school, for example, now insists on 'official' school trousers with the school logo, bought (and not inexpensively) from the school's own shop. This is a normal comprehensive school, not some kind of 'posh' private place. They use excuses like 'making sure parents have good quality clothes', and so on, but it's essentially a cash-making scheme to stop people buying cheaper clothes elsewhere, and I don't think schools should be doing that. I know it all adds to the school budget, but that's not the point - it costs parents money completely unnecessarily.
There is simply no need for all children in schools to look the same. Not only is it entirely unnecessary, but it sends entirely the wrong message to children about how they should regard 'difference' in other people. We are supposed to be preparing them for life, so is that really how we want them to be thinking? It would be folly to believe that they don't have their own 'codes' of what is 'acceptable' within uniform rules anyway - fashions change, but the way you tie your tie knot is just one example of how children will use particular aspects within the uniform rules to impose their own preferred kind of 'conformity', and base how they treat other children accordingly. We are encouraging this by having rules of conformity and encouraging such things as 'normal' and even 'desirable'. We are sending them the wrong message, and they are taking it on board for themselves. If we were to be sending the opposite message, that it's actually OK to be 'different', we would do much better in encouraging the idea that they shouldn't be bullying people for being 'different' in the first place, in my opinion.
There's another worrying lesson, though - that of 'authority', and how it should be regarded, exercised and treated. Children in school are not stupid - many can see that the rules are petty, and the enforcement of them is very often an exercise in draconian authoritarianism to enforce the idea that they must 'know their place'. I don't think that's a good lesson either. Obviously there are times in life where people have to accept something of a hierarchical structure between those who are charged with making decisions and those who have to carry them out, but that relationship should never be one of unquestioning obedience and petty exercise of 'power' without proper reasoning or explanation in that kind of way (with the possible exception of the armed forces, of course, because of the nature of that job, but the armed forces can train that for themselves - we really don't need everybody taught to be 'good little foot-soldiers' as children). All that message does is encourage 'rebellion' - the rules and authority are probably pointless and petty, so you should fight against them. I don't think it's great for children to be taught that they should always resist the rules or those charged with applying them - many rules in later life are there for good reasons.
There are some school clothing rules that exist for a reason, and that's fine. Having a 'no dangly bits in the woodwork room' is essential for safety - there's a very good reason for it which can be easily explained and understood. Likewise having school sports kits - you need to know who is on your team and who isn't! Even having a 'uniform' that exists to be used for things like school choirs is OK - where children are actually representing the school in some official capacity (and no, I don't buy the whole 'but they are effectively representing the school on their way home' idea either - it's just nonsense to justify the rules). It's no bad thing to have some basic guidelines of what's 'appropriate' for school, either - nothing too untidy, offensive, revealing, etc. - those don't need to be too harsh or petty, though. It's not a bad lesson for children to understand that they may need to wear certain kinds of appropriate clothes for certain kinds of activities and occasions, of course. That's not the same thing, though, as teaching them that 'conformity' in daily life is 'normal', and anything else that is 'not normal' is therefore 'bad'.
School uniform seems now to be an ever increasing spiral of 'conformity'. More and more schools seem to be making tougher and tougher rules. Primary schools are increasingly adopting compulsory uniform codes (something almost unimaginable outside of private schools when I was that age). I think we're in severe danger of bringing up generations of citizens who hold the deeply-ingrained idea that 'conformity' and 'normality' are 'good', and 'non-conformity' or 'abnormality' are 'bad', and/or that rules and authority are probably petty and therefore should be resisted. Enforced conformity to a uniform code is currently a very important part of their daily experience in growing up, so I think we need to think much harder about the messages we are sending to our children.