I would not use the treatment shampoo because it can be smelly, its pretty toxic, its expensive, lice are becoming immune to it and it will not prevent your son catching them again in the future (so you would have to buy more if he got them again). Instead use conditioner. Wash hair as normal, rinse, then apply conditioner and comb through with a 'nit comb'. If you part the hair as you do each section you can spot them more easily. The conditioner works by not allowing the lice to hold on to the hair, so they just slide off with the comb. Don't forget to check back a few days later. You can buy natural tea tree spray for hair as a repellant as lice don't like it. Hope this helps.

Not trying to disrespect the previous poster re treatment shampoos as I have used them in the past but would not buy them now as I prefer the natural approach.