"Gakkou e itta hou ga ii desu." ＝ you should go to school
~ suruhougaii means speaker's advice to his listener . so , this means the subject of the sentence with advice is "you"(anata) not I(watashi)
I should go to school = "watasi ha gakkou he ika-nakerebananai "
or "watasi ha gakkou he ikanakerebanarimasen"