INDIANAPOLIS (AP) — State officials are reviewing how students at 20 schools around Indiana were mistakenly allowed to use calculators on part of this year’s ISTEP standardized math exams.

The state Department of Education has tossed out scores for about 700 students in northern Indiana’s Rochester School Corp., where it says testing company Pearson incorrectly told schools to allow calculator use during an ISTEP section for which they weren’t permitted. The department isn’t certain yet how many students are affected at other schools.

Pearson says it regrets inadvertently providing inaccurate guidance.

The Education Department says the only students who will have to retake the math exam are some high school sophomores to meet graduation requirements. But the math scores labeled as “undetermined” could lower the state A-F ratings for those schools.