Pochter had emailed Gardner the letter to give to Justin, whom she and other camp staff have spoken with since Pochter's passing.
"Andrew cared for Justin deeply," Gardner said. "Justin definitely learned a lot from Andrew and I think vice versa. I think they were a good pair."
Pochter had been a volunteer at Camp Opportunity since 2008, Gardner said.
Camp Opportunity issued a statement on its website upon news of Pochter's passing, calling Pochter "an incredibly kind and compassionate young man."
"Andrew, we thank you for your personal contribution to a world where children are victims of birth and circumstance," the statement said. "Your sense of responsibility and servanthood reached well beyond your years. Many live longer than you, but few achieve true significance and achieve such personal greatness as you have."
The Pochter family declined to comment to ABCNews.com.