I have 3 girls, so needless to say every year when school would start they would come home with head lice within a week. My mother told me to use a shampoo and condition that has coconut as the fragrance. I have used Suave coconut shampoo and condition on them for 2 years now and they have not had head lice at all.
I also have a friend that does the same thing with her kids and it has worked for them. Guess the lice don't like the smell....don't know just know it works!