I started paying a school loan that I had just rehabing last month, it was always listed on my CR as 120 days late. Well today they put charge off. Why would they do this, is this hurting my score, more?

It is not clear whether you completed the rehab program or have just started it.

I just started rehabing, ade the 1st payment in March then they change it to say Charge off.

Is the charge-off being reported by the agency you are rehabbing with, or from the old lender you defaulted with?

What will happen: after you complete rehab, the collection tradeline with your current loan holder will be updated to closed & transferred, and they will sell your loan to a new lender you can start over with.