There is a really informative article here by Rachel Wareing about schools in Sussex, UK, implementing children's biometrics for these reasons:
Parents can see what their children are eating for lunch.
Teachers do not have to waste time taking a register. [!]
School librarians no longer have to issue books.
...others to see what reading habits our children have, by gender, age and ethnicity - sensitive information needs to be dealt with under the UK Data Protection Act.