TRENTON, N.J. — New Jersey’s top education official is resigning just as the school year is beginning.

Gov. Chris Christie announced Friday that Education Commissioner David Hespe is leaving his administration at the end of the month. No reason was given for why Hespe was stepping down. The governor’s office said he will explore opportunities in teaching and learning.

Christie said that the department’s assistant commissioner and chief academic officer, Kimberley Harrington, has been named acting commissioner.

Hespe, 56, said he’s leaving “with a sense of pride at all that we have accomplished together over the past few years.”

Hespe, who was confirmed as education commissioner in December 2014, oversaw New Jersey’s first foray into the Partnership for Assessment of Readiness for College and Careers, or PARCC tests. New Jersey, along with 11 other states first administered the tests in 2014. They proved to be controversial in New Jersey, with some parents boycotting the exams and arguing too much classroom time was spent on text prep.

Christie and Hespe announced last month that students’ 2016 PARCC scores had increased over the 2015 marks. They said it showed that students are on pace to be college and career ready.

The president of the state’s biggest teachers union, which clashed with the Republican Christie administration over the tests, said that despite disagreements with Hespe on policy that he was always accessible and willing to listen.

“I wish Commissioner Hespe well as he moves on to his next endeavor,” New Jersey Education Association President Wendell Steinhauer said.