"I love you Dave" was written on the balloon Linda Sanders let go to honor her husband, the teacher who died of wounds suffered while trying to rescue students during the attack on April 20, 1999.
"I'm just shaking, remembering that morning and I just want everybody to kiss their sons, daughters, loved ones, goodbye, every morning," she said.
The anniversary drew hundreds to a memorial service at Clement Park, next to the school.
"I feel like we are a stronger community, but a community that is still healing," said Columbine Principal Frank DeAngelis. "Even the scars will remain with us forever we will continue to heal."
Before the service began, Valerie Haile carried a cross dedicated to her friend, slain student Rachel Scott.
"I'm trying not to focus exactly on what happened that day, but remembering everybody that's gone," Haile said.
Thirteen crosses, one for each victim, were erected.
Haile did not attend Columbine, but she performed in a play with Scott two weeks before the teen was killed with 11 other students and Dave Sanders.
She said it was the first memorial service she had attended since the massacre committed by teen gunmen Eric Harris and Dylan Klebold, who committed suicide.
The sky was gray and temperatures were in the 40s as mourners trickled into the park all morning under the watch of light security.
Shanda McKown and her teen-age daughters, Amber and Brittany, placed a flowered blanket on the ground and bowed their heads in prayer a half-hour before the service started.
On a nearby hill above the school, parent Steve Schweitzberger scratched the words "never forgotten" into the cold dirt. His daughter, Sara, survived the attack and will graduate this year.
He said Columbine must be known for its recovery as much as for the tragedy itself.
"We're moving forward," he said.
Some scars were reopened this past week with the release of a report confirming that victim Daniel Rohrbough was shot by Eric Harris. Rohrbough's parents had believed he was accidentally killed by a Denver police officer.
The report did not settle two questions: why police had not arrested Harris and Klebold when threats they made against other students were reported, and whether SWAT teams were too slow to react.
A lawsuit has been filed on behalf of David Sanders' family, claiming he would have survived if SWAT members hadn't waited several hours to enter the school.