Irises
From the Frontline website:

This is one of the most requested programs in FRONTLINE's history. It is about an Iowa schoolteacher who, the day after Martin Luther King Jr. was murdered in 1968, gave her third-grade students a first-hand experience in the meaning of discrimination. This is the story of what she taught the children, and the impact that lesson had on their lives.

Watch this 46:00 program here in five consecutive chapters.

Thirty-four other Frontline programs can be seen -- in full -- here.