I have just arrived in this debate, so I am going to sidestep the intricacies of the validity of dreadlocks aspect, and dive straight into the OP -
Yes the school was wrong, because it has broken the law, been proven to do so, and made to retract the rule that broke the law.
I am absolutely in favour of school uniform, and the enforcing of basic uniform standards, which includes 'unusual' haircuts for either gender.
However, as the court ruled, this is not a 'fashion' haircut, it is an intrinsic part of this boy's expression of his faith, and, in the same way that other religious clothing and hair observances are permitted - this should be, and indeed now is.
The notion that this either 'attention seeking' or 'looking to undermine British culture' and similar points are utterly spurious.
Rastafarians can and do live amongst us, and it would be draconian and utterly backward-looking to start insisting that they wear their hair in a style that 'fits in' with British culture, since it is already clearly a part of British culture, and does no harm to anyone at all.
I have encountered a large number of musicians with dreadlocks, and to a man, they have been clean and healthy, as has been their hair.
If people think dreadlocks 'look dirty', that is their own subconcious racism kicking in - a fear of somethng that looks different to what they are used to, and because it is 'foreign', it must be bad.
The most salient point I have read thus far, is the one advising that this child had his locks when he joined the school, so why was no issue made then? Since the essence of dreadlocks is that they cannot be combed or cut, it is obvious that they are only going to grow longer!
Hopefully another 'uniform outrage' puffed up by the media and iminstepreted by vast swathes of the public, will die down, and we can get on with arguing about something that really matters.