Not much to be said about this outfit. To include a pop of color, I put it in the jeans instead (as you can see).

Leave the cardigan open and replace the belt.

Here, it's a crop top and I know they're generally not allowed in schools, but since you have a high waisted skirt, it should just look like a regular shirt. But, if you want to replace the top, I would suggest something that's poncho like, but you can also tuck in the skirt. Sadly, I could not find such an item on Polyvore. But I know you can find one at the mall or someplace.