It's obvious to everyone that fingerprinting children is wrong and a gross violation of civil liberties. Systems designed for the Military have no place in schools, and serve only to make money for private companies by infringing on the civil liberties of law abiding citizens.
Free consent can't be given by minors, nor their parents.
Common practice is for schools to request parental consent for fingerprinting when parents apply to the school of their choice. Parents naturally don't wish to 'rock the boat' by objecting to fingerprinting if they worry that their child won't get into the school they want for their child.
Companies selling fingerprinting machines should also not be allowed to claim 'we only use the fingerprint to generate a number', as all computers use numbers for everything they do – they're digital machines that can only use number sequences of zeros and ones.
Also, see my earlier post about government agencies being legally able to exchange information without consent. So fingerprints submitted to a school could legally be taken by another government agency without consent.