San Diego's school board has voted unanimously to take legal action after the Advanced Placement tests of more than 500 of the city's high school students were declared invalid because their seats were too close together.

The San Diego Unified School District Board of Education voted 4-0 Thursday night to take legal action against the College Board, which oversees the exams.

The College Board said last week it was invalidating AP tests taken at Scripps Ranch High because the arrangement of chairs violated the testing rules.

The move means 540 students will have to take the tests again, though they'll be offered for free.

The College Board did not claim any students cheated on the exams, which can gain students college credits by meeting the requirements for certain subjects.