Their presence on campuses is also a testament to the tenacity of families and disability advocates who, since the 1990s, when awareness of autism began to mushroom, have pressed for earlier diagnoses and interventions. Much of that battle unfolded in public secondary schools, leading to more services.

Over the last decade, officials at mainstream universities began realizing that growing numbers of spectrum students were being admitted — and, like Mr. Arnold, were foundering.

It was one thing for administrators to authorize accommodations like extra time on tests for students with dyslexia or attention deficit disorder. But how should they bolster students whose behavior was the primary expression of the disability — who could not stop shouting out answers in class and feared dorm showers?

And so the new autism support programs vary in emphasis. Some are based in disability resource centers, while others are in mental health offices, focusing on social skills and anxiety reduction.

“Our mission is to help them transition into the university, be successful here, and then transition out of the university to be successful in adult life,” said Pamela Lubbers, who directs one of the country’s most structured, coordinated programs, with 17 students, at Rutgers-New Brunswick.

Ms. Lubbers meets weekly with students, working them through a standardized “to do” checklist to help them identify small-step tasks to feel less overwhelmed, review their goals (“Describe the best social interactions you had this week”), and problem-solve. (“You think you left your I.D. on the campus bus. What steps will you take to find or replace it?”)

But even with support, these students often need extra time to graduate. Indeed, many do not make it that far. Some crumble under academic and organizational stress. Others succumb to campus allures like alcohol and drugs.