Showing photographs of head lice during health class discussions about recognizing and treating head lice infestations is useful, but not necessary. Lice are tiny, around 2 to 3 millimeters long, and very difficult to see. Children likely wouldn't recognize a louse if they saw it on themselves or another child.
Head lice are not dangerous, but many schools have strict policies forbidding children who are infested with the insects from coming to school. Many people believe that catching lice from another person is easy, but it actually requires direct head-to-head contact or sharing of hats and brushes with someone who is infested with the insects.
The most common way that an infestation is discovered is when the person with lice feels severe itching on his scalp. An inspection of the hair and scalp often reveals eggs, called nits, that are attached to strands of hair.
The social stigma associated with head lice often causes anxiety among school children, who fear being called out as "unclean" if it is suspected that they have lice. In reality, lice are attracted to clean hair, and although they prefer long hair, the insects infest those with short hair just as easily.
It is more effective to teach parents the signs of head lice than it is to teach children, as parents are the ones most likely to recognize an infestation, should one occur.