The Greens recently founded the Christina-Taylor Green Memorial Foundation, which supports academic, athletic and arts programs in Tucson schools.
"We don't want anyone to ever forget about her, because she was an amazing little girl," Roxanna Green said. "She did exceptional work in the nine years she was here, and that's what our story is about. It's an inspiring story, and it's a story of hope."
Even having grieved and memorialized their daughter so fully, John Green said "moving on" was a hard, complicated prospect.
"There's times when I'm, uh, almost afraid to move on ... or stop talking about her, because I know at some point the country is going to move on. That's why we thought it was important to tell this story, because there's going to be other tragedies in the world. ... But, right now our little girl is right on point, and people are learning things from her, so that, I guess that's a source of pride, and [there's] a sense of fear that, you know, some day that, that may go away."
Watch "Nightline" anchor Cynthia McFadden's full interview with the Greens tonight on "Nightline" at 11:35 p.m. ET