At some point in his past, Danny was trained in martial arts under Lei-Kung's tutelage in the mystical dimension of K'un-Lun. He finished his training when he faced the mystical dragon Shou-Lao, whom he defeated by punching the dragon's heart, after defeating the dragon he was imbued with its mystical powers, and became the Iron Fist.
Danny was a student at the Hell's Kitchen School for Troubled Youth.
Nick Fury's Trial
When Kingpin took over the Hell's Kitchen School for Troubled Youth, he imprisoned the students who didn't agree with his methods, Danny was one of those students.