SAN MARCOS, Texas — A high school principal in San Marcos has resigned after admitting that she changed up to 100 grades over two years.

Superintendent Michael Cardona said Friday that Kelli Lopez resigned earlier in the week as principal of San Marcos High.

He says grades submitted at the end of the school year were changed starting in 2014, the same year Lopez became principal of the school.

Cardona didn’t explain why the grades were altered, but said Lopez admitted to it when administrators confronted her after receiving a tip.

The school district has reported the matter to the Texas Education Agency. Cardona says students were not aware their grades were altered.