"To equate proficiency and advanced
performance rates across states and countries, we execute a crosswalk between
the NAEP and PISA tests by identifying levels of performance on PISA that
yield equivalent proportions of U.S. students as meet the NAEP proficiency and
advanced standards. To execute this crosswalk between the two tests, we assume
that all those who pass the NAEP proficiency bar in 8th grade will pass a similar
threshold on the PISA test the next year."

Comparing the NAEP to PISA is like comparing your blood pressure to your cholesterol. Other than the fact they both measure something about your body, they aren't the same. NAEP and PISA are different in design, item analysis, and sampling methods. Neither are "aligned" with all the different state and international curriculums. In other words, this article seems to have a political agenda (typical at Harvard) before it starts.

Can we make accurate international comparisons? Yes, but it's a stretch to go from this flawed methodology to broad conclusions. Paper pencil tests like these are limited comparisons at best.

Always question #1 when it comes to ed research.

Every study of educational performance, done in the last 50 years, has concluded that income was the best indicator of success in the classroom. Our nation's increasing level of inequality and reform movements designed to segregate high achieving students from their less successful peers are the problem.