Altering the wall color and decoration can make a big impact with little dough. If your tween daughter has grown out of her pink princess phase, a coat of marigold, sage or light teal paint might do the trick. Boys might like more masculine tones, such as navy blue and forest green. Chalkboard paint that you can write on might also appeal to tweens.
If you're worried your tween's taste will change soon after the paint dries, many stores offer a variety of wall decals and temporary stickers that are good alternatives to wallpaper. They come in various geometric shapes and silhouettes for boys and girls. You can also hang tapestries or interesting fabrics to serve as backdrops for beds or accent walls.