An 8th grader can wear jeans with a decent top to school. You can wear anything that you feel comfortable in. If you love dresses, look for a beautiful one. Wear something that will describe your personality.
Wear something that is comfortable. Do follow the dress code, and don't let other people bring you down about that. If your clothes are clean, wear them! No need to dress like an adult, save that for when you are one! Jeans are good, and so are graphic tees so you can show off what you like, and whatnot. Shop at casual stores that aren't too expensive. Get your mom to take you shopping, but tell her that you want to pick stuff out, and chances are if she likes it, she might buy it, so this can save you money as well. Have fun in 8th grade. Its a really good year.