San Marcos High School’s principal has resigned after admitting to altering grades, the district said.

San Marcos CISD said in a letter to parents that Kelli Lopez announced her resignation on Sept. 28. Superintendent Michael Cardona told KVUE Lopez submitted the following statement to the district:

“I do not know exactly how many DOC’s [Document for Change Forms] were submitted in total….it may have been approximately 40-50 each year for an approximate total of 80-100.”

Cardona added that the forms were submitted in the 2014-15 and 2015-16 school years.

San Marcos CISD said Dr. Bobbie Turnbo will serve as interim principal at San Marcos High for the remainder of the 2016-17 school year. The district added that Turnbo has 41 years’ experience in education, including as principal at the middle and high school levels.

GO HERE to read the full letter home to parents.