To all those calling for 'one rule for everyone', we already have one, it is the section in the human rights act that refers to article 9 of the EU charter of human rights, which states:
Which basically means that until you can present solid evidence of kirpans in schools being used for naferious purposes, you have no grounds to ban it.
Given the nature of the Kirpan within the sikh religion, it is quite correct that neither the government, nor local state service providers, can ban it at a whim. Trying to make comparisons with crucifixes and the like only shows fundamental misunderstandings of all the religions involved in the comparison.