Most kidnappings are committed by non-custodial parents, and schools are an easy place to conduct such a kidnapping. So yes, scanning drivers' licenses at school does serve a purpose, even if it doesn't apply to your child.

http://abcnews.go.com/US/story?id=91365&page=1&singlePage=true

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According to statistics cited by the NCMEC, most missing children are abducted by relatives or parents: a soon-to-be released report, the Second National Incidence Studies of Missing, Abducted, Runaway, and Thrownaway Children, referred to as NISMART-2, finds that 203,900 kids were abducted in 1999 by family members or parents. Approximately, 58,200 were "non-family" abductions — only 115 were defined as the frightening kidnappings by strangers.