After Hurricane Katrina hit New Orleans in 2005, Tulane University made volunteering for community projects in the ravaged city, such as restoring parks or tutoring grade-school students, a requirement for graduation. Since then, applications to Tulane have shot up. Schools and colleges nationwide have increased volunteer opportunities for students, and nearly 90 percent of colleges offer service-learning programs that tie class work with volunteer activities. Researchers see ample evidence that at least some service programs encourage students to participate in civic life as they grow older. Experts worry, however, that volunteer opportunities are far more prevalent for middle-class and affluent students than for those from low-income families. Meanwhile, many school districts continue to mull whether to require volunteer service for high school graduation. Courts have upheld the constitutionality of such requirements, but some students and parents resist them.