My 16 yr old daughter is coming up for exams in 4 weeks time. She is a bright girl but is not revising and does nothing but talk to her friends on her mobile and social media. I have set her a target to give me her phone at 10pm each night and her wifi is limited and she has gone mad. Is this unreasonable? She is my 4th child but times have changed so much in 10 years and I am struggling to know what to do for the best.