Thirty years after the killing stopped, Cambodia suffers from a particularly painful generation gap — between those who survived the brutal rule of the Communist Khmer Rouge and their children, who know very little about it.

“I used to tell my children the stories, but they only believed a tiny bit, like nothing,” said Ty Leap, 52, who sells noodles and fruit drinks from a roadside stall. “I don’t like it, but what can you do? It really is unbelievable that those things happened.”

As much as 70 percent of Cambodia’s population is under the age of 30, and four out of five members of this young generation know little or nothing about the Khmer Rouge years, according to a survey last fall by the Human Rights Center, University of California, Berkeley.

That ignorance — among both young and old — seems also to embrace the trials of five major Khmer Rouge figures that began last month, a process that is meant, in part, to begin a process of healing and closure.

Because of these cross-currents in recent Cambodian history, the Khmer Rouge period has not been taught in school, causing some teachers who are survivors to feel orphaned by their students.

A new high school textbook has been prepared but will reach only a portion of the country’s students.