|England and Northern Ireland-United Kingdom||●|
|Korea, Republic of||●|
|● = Indicates participation in particular assessment with results reported or forthcoming.
○ = Indicates participation in particular assessment but results either not reported or reported separately, typically due to sampling, response rates, or other procedural problems with the data.
NOTE: OECD member countries are bolded. Subnational education systems are italicized.
SOURCE: Organization for Economic Cooperation and Development (OECD), Program for the International Assessment of Adult Competencies (PIAAC).