WASHINGTON — The pass rate on rigorous Advanced Placement tests went up by 72 percent last year at high schools that took part in a National Math and Science Initiative program that trains teachers and gives students extra help on Saturdays.

The program has been especially helpful in boosting success for girls and minority students — groups that have been under-represented in advanced math and science classes, said initiative CEO Sara Martinez Tucker. The nonprofit group announced its 2012-13 results Wednesday.

Katherine Hergenrether, a chemistry and calculus teacher who was involved in the training in Oklahoma, said part of the value of National Math and Science Initiative support for AP was that it raised expectations.

When students see teachers working hard to offer the college-level classes, “they step it up as well,” Hergenrether said in a conference call with reporters.

The group’s AP program last year was in 551 high schools in 19 states, or about 2 percent of the nation’s schools. It will be added in schools in Mississippi, Alaska and Tennessee this year. The program began five years ago and has improved the pass rates on the AP tests every year, Tucker said.

Each participating school receives the extra support for three years at a cost of $500,000 per school. Some school districts receive funding as a grant from the group, which gets support from foundations, corporations and the U.S. Department of Education.

The program includes “extensive teacher training,” a mentor for each teacher throughout the school year, help for students in Saturday sessions and awards for teachers and students, said Gregg Fleisher, the group’s AP program director.