Re: does anyone know what would happen if I tell my school about the cutting?
I think in the very least your school would tell your parents about your cutting. Depending on the severity of your cuts, you may have to go to the hospital to get stitches and/or prevent infections from developing. I think social services would only take you away if they suspect you're being abused or neglected.
In any case, I think talking to someone, whether it be someone at your school or your parents about your cutting is a good decision. Getting the support and help you need to develop healthier coping mechanisms will be beneficial in the long-term.