Is there a way to keep your hair straightened for a whole day?

ok my hair is annoying it will be straight fer bout an hour then it either goes in or out on the ends or it goes kind of poofy and its bothering me cuz skewls bout too start and i dont want thiss too happen at skewll so anyy ideaas on how to keep yur hair straight fer atleast a day better yet over night too?? please helpp me out!!!