Head lice are acquired from other infested people. Upon learning of their child's infestation, parents frequently seek to ascribe blame. This 'knee-jerk' reaction is understandable but unproductive. The offending lice came from some other person, but it is not currently possible to determine the identity of the donor. Parents are encouraged to focus their energies on education and treatment rather than on unsuccessful, time-cosuming witch-hunts. Rather than accusing school administrators or other parents for not preventing the spread of head lice, parents are likely to benefit more by ensuring all children and adults in the home are inspected and treated as appropriate.
Egg of Pediculus humanus capitis in comparison with a match
Photo by Pediculosis (Deutsche Pediculosis Gesellschaft e.V.) [GFDL or CC-BY-SA-3.0-2.5-2.0-1.0], via Wikimedia Commons