New test results place American high schoolers well below their global contemporaries in mathematical literacy. The Program for International Assessment 2015 scores, released Tuesday, confirm a downward trend that appears to track the rocky implementation of the Common Core State Standards.

PISA tests how well fifteen-year-olds stack up against their global contemporaries. In math American teens rank 20 points lower than the international average—and 12 points lower than their own 2012 average. A yearly exam, the PISA rotates between reading, science and math so that a comparative ranking of the world's teens rolls out once every three years in each subject.

Science and reading have held steady while math has, disturbingly, tanked. "We're losing ground—a troubling prospect when, in today's knowledge-based economy, the best jobs can go anywhere in the world," said Education Secretary John B. King Jr. regarding the PISA results.

The Common Core State Standards for high school math expressly emphasize teaching applied math skills through practical problem solving. And yet we're now, as a nation, in the bottom half of 72 participating regions and countries when it comes to applying our math skills to practical problems, known as "mathematical literacy."

There's no saying at this point whether the math standards themselves precipitated the downward trend, at least according to Andreas Schleicher, director of education and skills at the Organization for Economic Cooperation and Development, the member organization administering the PISA. "Common Core concept is quite well aligned with what we see in many high performing education systems," Schleicher told The Hechinger Report.

Common Core's math plank in particular has been one of the least popular, and possibly least effective, elements of the controversial standards' implementation—and not just because " new math" is a hard sell.

Jon Star, an education psychologist at the Harvard School of Education who specializes in children's learning of mathematics in middle and high school, called the downward trend in math at the high school level "disappointing but not surprising."

The trouble is that the standards, Star said, were designed with elementary and middle school students in mind: "It's not surprising that some of these interventions have had minimal to no effect in high school—because that's not really who they were intending to effect."

"The math you learn as a seven-year-old is different in fundamental ways from the math you learn as a fifteen-year-old. [In education reform] that doesn't seem to come up."

Math standards at the high-school level may build on conventional topics and call for instructional techniques students will recognize from younger grades. But they also extend a pedagogical approach up into the high school classroom that does not fit what many teachers know—and know to work.

Group problem-solving may not lend itself to a many high school teacher's typical algebra lesson, for instance. High school math instruction has remained a sore spot in decades of ambitious education reform; and it doesn't help that working through problem sets will never quite qualify as a progressive teaching practice, even if it remains the best way to master a math formula.

Middling high school math and science scores have consistently been a foremost impetus for reforms to prepare American youth for competition in a STEM-heavy workforce. At the time of their nearly nationwide roll-out, the Common Core mission statement read: "With American students fully prepared for the future, our communities will be best positioned to compete successfully in the global economy."

The goal of readiness for global competition is ingrained in the reforms—the federal grant program that incentivized states to adopt the Common Core standards was even called " Race to the Top." And yet high school students, perilously close to their entry into "our global economy," are coming up short. These latest scores indicate not just that the race started off with some initial stumbles. But that it may have started off in the wrong direction entirely.