Ideas for bottoms:
Bermuda Shorts
Capri pants
Mid-length or calf-length skirts (tiered skirts, like gypsy style)

Now for tops... I assume that by "Sleeves must go down to the shoulder" you mean "not sleeveless". In that case, polo shirts or shirts with cap sleeves are definitely a must. You could also wear blouses with puff sleeves, or loose tops with three quarter sleeves. If you need coverage, you could always go for a light jean jacket or something like that,

puff sleeved shirt, over the knee socks, patent leather shoes and a cute skirt lol... but thats just me

I'm starting high school too! But we dont start until next week.
Anyway, I'm wearing my white cuffed bermuda shorts from Delia's and I'm not quite sure what top I'm wearing yet but probably a tank top or this this plumish flowy shirt from AE that tightens at the bottom.

And I will probably wear a cute headband or bracelet or earrings. They have really cheap skinny plastic headbands at Target that look good with lots of outfits and then they work well for keeping my hair out of my face at cross country practice after school!

Also, its good to look nice your first day of school but its also cool to save some of your best outfits for the end of the week/second week so when everyone else is running out of cute outfits, you'll stand out b/c you look super cute!! haha im going to try that and see how it works!

And, if you need a jacket for indoors, a cute hoodie or cropped sleeve cardigan works well!

hi! i'm done with high school but i think that you shouldn't try look like every other girl. what i mean by that, i mean by CLOTHES! you can get clothes for cheap but still make it look really nice, without looking like you tried hard.