One important point, that has been reiterated time and time again by biometric vendors, Jim Knight and the ICO, is that the biometric systems in schools cannot reverse-engineer a fingerprint.
This does not seem to be the case according to Kim Cameron's recent weblog, Architect of Identity and Access in the Connected Systems Division at Microsoft, entitled "Paper argues biometric templates can be reversed". It shows that reverse-engineering a digital fingerprint may just be possible. He cites this paper "Can images be generated from biometric templates" by Andy Adler, University of Ottawa, 2003.
Also see these Research discussions at West Virginia University from 2005 "We show that minutiae information can reveal substantial details such as the orientation field and the class of the associated fingerprint that can potentially be used to reconstruct the original fingerprint image."
Both of these papers are not too recent and since then one would presume that the technologies in this field have advanced.
However, even thought the possible reconstruction of a fingerprint seems relevant to the argument of biometric technology in schools, ownership and possible 'loss' of ones digital fingerprint is still very relevant... who has access to it, the systems it is on, how it can be used (or abused). These are the points that should be seriously considered by children (and parents) as they unwittingly give up their biometric data for systems in schools which are non essential for purchasing food or accessing library books.