AIɫɫ

Many high school students struggle to understand the relationship of unemployment and inflation through the Phillips curve — even those who are taking the college-level Advanced Placement course in macroeconomics.

Others stumble on electromagnetic fields in AP physics. Or they get lost in area and volume analysis in AP calculus.

Now educators are exploring a way to help students across the country, and around the world, master such difficult concepts through online lessons posted on a Web site that specializes in delivering college-level courses for free.

On Wednesday, AIɫɫ in North Carolina announced a partnership with edX — a Web site overseen by Harvard University and the Massachusetts Institute of Technology — and the College Board that will create lessons for some the toughest subjects in those three AP courses. The nonprofit College Board oversees the AP program.