The admins in my school are not fans of having tons of store bought posters all over the room. I have a hard enough time getting the students to pay attention to the meaningful ones I make and put up I can't imagine they'd ever read or learn from something I hung up on the wall just to make the room look pretty. Other than bulletin board board paper and boarders there is very little that can go up in my room until the students start. What's on the walls is their work or my work. I wouldn't worry about it now.