you have a lot to learn if you think teenage boys won't stare at your tits- how old are you by the way? teenage boys will look at any tits on anyone under 60 so if you are 20s you are fair game.
Did you never see boys at school drop pencils on the floor so they could look up the teacher's skirt when she walked past???!!!
I taught in sec schools for years and lewd comments/thoughts about female teachers from male students go with the territory.
I don't think you are getting a lot of conflcting advice- only 1 person has said yes to leggings or chinos.
basically think how you would expect a bank manager, solicitor, or office manager to dress for work.
As someone else has said you need to think of having 2 wardrobes-work wear and casual wear.
For your week in school you should be wearing smart work trousers, or a smart knee length skirt .
my 22 yr old daughter is fashionable but has a pair of black trousers from Next for interviews and a black knee length pencil skirt, which she wears with a nice white shirt.
You are only there for a week, so quite honestly one pair of trousers, a skirt or dress and a few smart tops should see you through the week.