Nearly 75 percent of Montgomery County high school students’ Advanced Placement exams earned a college-ready score of 3 or higher in 2012, placing the county near the top of national achievement lists with scores that were nearly 18 percentage points higher than the national average.

A record number of Montgomery high school students took the exams this year, and the county was one of 539 school districts out of more than 12,000 across the United States and Canada that boosted the number of students both taking AP exams and scoring passing grades.

The distinction landed Montgomery County on the Third Annual AP District Honor Roll and maintains the county’s reputation as having one of the top school systems in the nation for AP participation, access and performance.

“It’s a remarkable achievement,” said Trevor Packer, senior vice president of the College Board’s Advanced Placement Program. “It’s not something that typically happens.”

Prince William County also landed on the AP District Honor Roll this year, and Prince George’s County saw marked improvement over the past year, with a nearly 10 percent increase in the number of tests that received a passing score.

The tests, issued across a spectrum of academic subjects, help measure how well students are prepared for college and the workforce. High school students who score a 3 or higher on an AP exam’s five-point scale can earn course credits at most colleges and universities, potentially saving students time and tuition as they complete undergraduate degrees.

Nearly 16,800 Montgomery County students took more than 32,970 AP exams in 2012, an increase of 537 students and 1,240 exams over the previous year, according to data the school system released Wednesday. Exams that scored a 3 or higher increased about 3 points over 2011; Montgomery’s average passing rate of 75 percent is well above Maryland’s average of 61 percent and the national average of 57 percent.

Prince George’s County saw a huge boost in the number of Hispanic students taking and passing AP exams — with an increase of 18 percentage points in participation and an increase of 45 percentage points for those scoring a 3 or better. Both numbers far surpass national and Maryland figures for improvement.

Prince George’s schools spokesman Briant Coleman said the county’s rising Hispanic student population and the increasing rigor of the school system’s curriculum are responsible for the trend.

In Loudoun County, students took more than 14,000 AP exams, with 57 percent of the exams earning at least a 3. Alexandria’s high school, T.C. Williams, set school records with a total of 785 students taking 1,623 AP exams. As of Wednesday, D.C. public schools and Arlington and Fairfax counties did not have data available.

Montgomery County Public Schools Superintendent Joshua P. Starr attributed his school system’s improvement to the district’s focus on making sure students across racial and socioeconomic lines are pushed to prepare for college at all grade levels.

Montgomery has long encouraged students to take Advanced Placement courses, and the school system includes a passing score of 3 or higher on AP exams as one of its “Seven Keys to College Readiness.

There is still an achievement gap in Montgomery, with 81 percent of white students and 79 percent of Asian students earning passing scores; their black and Hispanic peers performed at least 20 percentage points lower. But Starr said it is compelling that participation and performance increased for black and Hispanic students.

“That is powerful because there are still people out there who say if you let too many kids in who aren’t prepared to take AP exams, scores are going to go down,” Starr said. “The data show otherwise: When you open up doors and you support kids, you get good results.”