TRENTON -- An enthusiastic testing "opt-out" movement, fueled in part by the state's largest teachers union, cost New Jersey taxpayers more than $1 million in 2015, according to the state Department of Education.

New Jersey paid testing giant Pearson $1.4 million for tests not taken in the first year of the PARCC exams because it overestimated the number of students who would take the math and English tests by nearly 60,000 students, state auditor Stephen Ells found in a report released this week.

The education department said in a written response to the audit that the estimated number of students taking PARCC was based on previous years of testing. It attributed the million-dollar mishap largely to parents who held their children out of testing.

"An unforeseeable number of parent refusals reduced the number of test-takers, accounting for the disparity in the estimated number of tests and the number of tests actually taken," Assistant Education Commissioner Karin Garver wrote to Ells.

Because New Jersey's estimate was not within 2 percent of the actual number of students who took the tests, it was contractually obligated to pay for the number of tests it originally ordered, according to the department's response to the audit report.

PARCC tests were supposed to cost New Jersey about $25.50 per student, the Department of Education said in 2015. The state paid Pearson a total of $20.8 million for the first year of tests for grades 3-11, called the Partnership for Assessment of Readiness for College and Careers exams.

In the months leading up the computerized exams, parent groups and the state's largest teachers union, the New Jersey Education Association, sharply criticized the PARCC tests as unproven, overly confusing and unduly time consuming. The NJEA waged an expensive advertising campaign that included television spots featuring parents nearly in tears over standardized testing.

Though the state never released an official tally of students who opted out of testing, data shows that more than 130,000 students did not participate in the exams. The majority of those students were likely opting out but some also missed testing for other reasons, according to the state.

Steve Baker, spokesman for the NJEA, said teachers who opposed PARCC and parents who refused to allow their children to take the tests are "absolutely not" responsible for the $1.4 million.

"If the Department of Education had spent more time listening to parents and less time insisting that parents love PARCC, they might have been able to save that money," Baker said.

The audit report suggests stronger oversight of the PARCC contract.

It also calls for stronger background checks of Department of Education employees who visit schools and enhanced oversight of the daily work schedules of department staff.

Currently, state staff who visit schools are not subject to the same background checks as school employees. The department currently requires all employees to work seven hour days but has no limitations on when those hours must be worked, the audit found.

Adam Clark may be reached at adam_clark@njadvancemedia.com. Follow him on twitter at @realAdamClark. Find NJ.com on Facebook.