K-12 names the long stretch of school in the United States that runs from kindergarten through grade 12 — about ages 5 to 17. K is kindergarten; 12 is the last year of high school. In American talk, K-12 education means that whole block, as opposed to college. Public K-12 is paid for by the government, so families do not pay school fees to send a child to a public school. Though actually, that tidy picture is tidier than life: some children go to private school, or learn at home, and those paths are not free from the state in the same way. You will see K-12 in news and government talk, not in the playground. Taiwan’s 十二年國教 covers a similar number of years, but it is not the same system under an English nickname — K-12 is how the US (and sometimes Canada) points at that span.