Microsoft Corporation chairman Bill Gates says U.S. secondary schools are "obsolete," and he warns that American students are not being educated to effectively face growing competition in the global economy.

Featured as the keynote speaker at a meeting of U.S. governors about the state of the country's high schools, Mr. Gates said Saturday that the American secondary education system has not changed substantially in the past 50 years, when schools were designed to meet the needs of a different age.

The billionaire philanthropist has donated more than $700 million to reinvent American high schools through his charitable foundation the Bill and Melinda Gates Foundation.

In a speech here in Washington, Mr. Gates said the United States ranks 16th out of 20 developed nations in the percentage of students who complete high school, and only 14th out of the top 20 in college graduation rates.