Massachusetts education officials have closed their investigation into irregular test scores at a Springfield elementary school.

Last year the state invalidated three years of test scores for Dryden School in Springfield because of significant inconsistencies in student scores and “widespread” eraser marks in test booklets, with incorrect answers changed to correct ones.

A state education spokesperson says after an “extensive investigation” officials could not determine who changed the answers. She says the Dryden principal from those years has surrendered her educator’s license, but that it was voluntary and not part of a disciplinary action.

Springfield Schools Spokesperson Azell Cavaan says the district all along had confidence in Dryden’s staff.

“We certainly know that students are told to check and recheck their tests,” Cavaan says. “And so we know that there could be a…perfectly reasonable explanation why there would be erasures on a test other than any sort of impropriety.”

But she says the district is not contesting the state’s decision to invalidate the scores.