Boston College professor Karen Arnold encountered a mystery in her investigation of graduates of an innovative high school program in Providence, R.I. Many of the disadvantaged students had lied to their former counselors about starting college, making the program look better than it was.

Why?

The Metropolitan Regional Career and Technical Center, a network of small high schools usually called the Met, had a splendid record for getting struggling students ready for college through a series of internships that promoted academic, social and emotional development. Its graduation rate was consistently more than 95 percent. Nearly every graduate was accepted to college and 75 percent of them reported that they had enrolled.

But when Arnold, asked by the Met to get a clearer picture of its graduates, checked enrollment status in 2006 with the National Student Clearinghouse, she discovered that about a third of the program’s alleged new college students were not actually registered. She learned that the summer months before college had been too much for them. They didn’t understand the enrollment paperwork. Money problems emerged. Their parents and friends opposed their plans. They couldn’t bear to tell the Met counselors who checked up on them that they had not followed through.

Arnold’s bombshell revelations, and similar discoveries in other cities, have inspired one of the most incisive books written about the American college admission system — “Summer Melt: Supporting Low-Income Students Through the Transition to College” by Benjamin L. Castleman and Lindsay C. Page. It will be published in October by Harvard Education Press.

Castleman and Page calculated that “as many as one in five high school graduates who have been accepted to and intend to enroll in college fail to matriculate anywhere in the fall semester as a result of unforeseen challenges they encounter during the summer.” Until Arnold’s research, no one knew this. It was assumed that if disadvantaged students sent their deposits by May 1, reserving the college spots they worked so hard to get, they would be on campus in the fall.

The authors called this phenomenon “summer melt,” borrowing a term that college admissions officers have previously used for students who switched to another college after paying their deposit. In some school districts, the authors found, as many as 40 percent of disadvantaged students who paid their deposits failed to matriculate anywhere. “It would be more appropriate to refer to this as a ‘summer flood,’ ” the authors said.

Argelia Rodriguez, head of the nonprofit District of Columbia College Access Program (DC-CAP) that does college counseling for the D.C. public schools, said 75 percent of the students it tracks from both regular and charter D.C. schools send in their deposits, but only 62 percent are verified to have enrolled in the fall.

One problem, Castleman and Page said, is the paperwork flooding the homes of disadvantaged students in the summer when they lack easy access to the teachers and counselors who helped them prepare their applications. Many of them “had yet to fully internalize the dream of going to college,” the authors said. “They were torn between the desire to further their education and the lures of home, staying with a girlfriend or boyfriend, receiving a steady paycheck, and continuing to contribute financially and otherwise to their family.”

Arnold and Castleman told me “lying” was too strong a word for what the students did. The students were overwhelmed, they said, and did not intend to mislead. To me, the book makes clear that the word applies, and explains well why they did it.

The authors describe the methods being used at the Met and elsewhere to end summer melt. Rodriguez said helping admitted students with last-minute details is part of DC-CAP’s work. It will take more research to see whether that is enough to cure this unexpected epidemic of panic in August.