The fatal shootings at Northern Illinois University this month were shocking yet familiar. For the second time in 10 months, a student with a record of mental-health problems went on a killing spree at a large public university. Ever since a disturbed student fatally shot 32 students and professors at Virginia Tech last April, college administrators nationwide have been pumping more money and resources into efforts to prevent a similar tragedy on their campuses. Administrators have updated their emergency-alert systems and refined their crisis-management plans. They are working more collaboratively with their mental-health staffs and other groups on their campuses to identify at-risk students. But colleges cannot keep up with the rising demand for mental-health services. And disagreements over exactly how to handle at-risk students have stymied efforts to allocate limited resources. The International Association of Counseling Services, a nonprofit accrediting organization, recommends that colleges have a ratio of one counselor every 1,500 full-time-equivalent students. The average ratio, according to 2007 data, was one counselor per 1,969 students, and 85 percent of counseling centers reported that more students were arriving at their centers with significant histories of mental-health issues.