That's what this Wikipedia chart says:
List of rampage killers: School massacres
It's interactive, you can have the chart sort by any of the headings. If you click on "Country," it will sort alphabetically by country.
21 incidents in China from occurring 1995 through 2012
17 incidents in the U.S. occurring from 1927 (yes, that's 1927 ) through 2012.