All are nonviolent offenders, as are about two-thirds of prisoners over all. They spoke on condition that only their first names be used.

Sing, a tall, slim man in his early 40s, has been in prison for 15 years on drug charges, with two years to go. His son and daughter are now 17 and 23, but he has been “adamant” about staying involved in their lives — through letters, phone calls and emails.

“They are doing very well,” he said. “They have no criminal problems.”

Yet because they live in Florida, 1,000 miles away, Sing hasn’t seen them in five years. He and other inmates expressed frustration at how often the Bureau of Prisons flouted its official policy of trying to house inmates in facilities within 500 miles of their families. The authorities are supposed to do as much as possible to keep families together, Sing said bitterly, “but they do more to keep families apart.”

Other inmates said that no matter where it was, prison had a way of corroding emotional ties to the outside world. Jon, who is 55 and three years into a five-year sentence, scoffed when he first arrived and a seasoned inmate told him he’d soon stop caring about the everyday concerns of the people he left behind, including those of his only child, a teenage girl.

The veteran, Jon sighed, was right. “I have to make a special effort now to stay emotionally connected with my daughter and to keep up with her daily experiences,” he said. “It’s hard for me to do. She’ll start talking about her friends and I’ll have no idea who they are.”

Perseverance helps. “My top priority is to stay relevant in my kids’ lives,” said Rob, an athletic 46-year-old who has been in prison four years and has three teenage daughters. “I put them first as much as I can.”

He calls each girl once a week and prepares conversation notes ahead of time. He sends gifts he’s drawn or crocheted. They have a family book club. His daughters seem to be doing well: One is at Bryn Mawr College, and another is at Tabor Academy, a highly competitive prep school. But with nine years of hard time yet to go, who knows if all the threads will hold?