Frederick Douglass - probably people will pick him but he was a brilliant man, strong in character and intelligence
Sojourner Truth - Amazing orator, feminist, one of my first heros of youth - possibly because at the time I was fascinated with her height (I was like 8 at the time)
Madam CJ Walker - Entrepreneur, successful in rough times (I’m reading a book written by her great great granddaughter right now)
WEB Du Bois - Brilliant mind, sociologist, interesting discussion of race, interesting to talk of his relationship and differences to Booker T Washington (also brilliant mind)
Langston Hughes - PHENOMENAL poet, 'nuff said.
Ralph Ellison - writing that would move you to tears
Nikki Giovanni - Great current poetwho came of age during the 60s and 70s and has sharp take on more current race relations
Gwendolyn Brooks - another fantastic poet
Just some of my favorites. If you son was interested, some of the Black Power movement guys (Cleaver, Carmichael, etc) or even Malcom X (the autobiography is fantastic!) would be interesting to talk about in regards to how and why they split from MLK and how they began to feel by the 60s. I did a report like that in 10th grade.
I don’t know why the kids in his class would feel animosity toward him for talking about people who don’t always get taught about in school. I was one of three white people in a college discussion section in my African American History class. One of the guys asked us (the white kids) how we felt learning a different, and at times more negative, perspective on American history than what is commonly taught in high schools. He seemed generally surprised and pleased to find out that we all came in knowing a decent about about this part of history. But then again, that was college, not junior high. 
Okay, I’m officially a bookworm. I’ll just stop talking now. I hope my rambling helped!