One minute your sweet child is begging you to come on the class trip or to lie down with her while she falls asleep. Then, seemingly overnight, she starts treating you like dirt, discounting everything you say and snickering at your suggestions. If you look closely, you'll see that you've been through this before, when she was a toddler -- only instead of shouting "no!" like a two-year-old would, a teenager simply rolls her eyes in disgust.