You'll add a hook later! For now, focus on your THESIS (author's position plus your three reasons!)
Put your WEAKEST reason first! That way, if people forget it, NO BIG DEAL! Still, be sure you back it up with proof!
Maybe here is where you want to add your REBUTTAL and COUNTERCLAIM
"Some people say that cell phones don't cause children to be overweight, but, according to my poll of 150 students at Countryside, more than 87% of students prefer playing on their phones to playing outside!"
Just copy your thesis into your conclusion! Your CALL TO ACTION tells your reader what you want him/her to do!