Bangladesh, Dec. 3 -- American students may not be reading any better, but they're moving up in rankings of educational achievement worldwide because many of their peers in other countries are performing worse.

And while their math performance may not be declining, 15-year-olds in the United States still lag the scores of their peers in dozens of other countries.

Overall, the latest global snapshot of achievement shows American students scoring above average in reading and science, but below average in math.

The 2018 Program for International Student Assessment, or PISA, shows several Asian school systems at the top. The best-performing across all three measures was a group of four Chinese provinces - Beijing, Shanghai, Jiangsu and Zhe...