The chancellor of the nation's largest public school system vowed to fail elementary school students who have not mastered basic skills.

Chancellor Rudy Crew said Monday that, beginning in the spring of 2000, he wanted to hold back fourth- and seventh-graders who do not perform at their grade level, The New York Times reported Tuesday.Crew said he wanted to give schools two years to identify at-risk students and provide intensive remedial help to avoid wide-scale failures.