Maureen Pappachristou defeated Daniel Cox in a Glen Cove special election last night and will replace former school board member Joel Sunshine on the seven-member board.
Pappachristou received 330 votes to Cox's 191 votes in the election, which was held at Finley Middle School in Glen Cove.
She takes over for Sunshine, who moved out of the district over the summer. The term ends June 30.
Voters made their selection as the district reels from allegations of test-fixing scandals at two elementary schools and its high school.
An independent investigation found that 22 teachers at Connolly and Landing elementary schools helped their fifth-grade students do better on exams, by means including supplying correct answers and filling out answer forms.
In other instances, teachers recommended students reconsider their answers to questions on state English Language Arts and mathematics exams in spring 2012.
The district faces separate accusations of test-changing on 2012 Regents exams at Glen Cove High School.
The report on the elementary schools found that nearly 85 percent of the 60 children interviewed "indicated they received inappropriate staff-directed assistance" on either the English Language Arts or the math test, or both.
The accused teachers denied they had inappropriately assisted the students, the report said.
The State Department of Education and the Nassau County district attorney's office also are investigating the allegations.