Ava DuVernay thinks it's ''incredible'' her Netflix documentary '13th' is showed in schools.

The 45-year-old filmmaker helmed the documentary which tackled racism in the US penal system back in 2016, and DuVernay said it was a ''really tough couple of years'' as she had to look through ''hours of racist, violent footage''.

Speaking to Time Out London, DuVernay said: ''It's been incredible. It's assigned in schools and it's always showing on a big screen somewhere.

''It was a really tough couple of years making it. I had to look through a thousand hours of racist, violent footage.''

DuVernay also said helming the documentary pushed her to direct the new Disney movie 'A Wrinkle in Time' and also said how she related to the main character Meg - played by Storm Reid.

She said: ''That was one of the things that pushed me towards 'Wrinkle'. It was a self-care thing.

''[The book] missed me. I don't know how, because my sister read it and I was in the same bedroom.

''But when I read it, I was really captivated by Meg, this girl with glasses who didn't think much of herself and who's lonely in the world.

''I related to her. When Disney said they were open to making her a black girl that took it there for me.''

The film - which is based on the 1962 novel of the same name by Madeleine L'Engle - follows Meg Murry [Reid] who works with her highly intelligent brother and fellow student Calvin O'Keeffe [Levi Miller] and three astral travellers Mrs. Which [Oprah Winfrey], Mrs. Whatsit [Reese Witherspoon] and Mrs. Who [Mindy Kaling] to rescue her father Alex [Chris Pine] who is being held captive on a distant planet.

DuVernay - who worked with Winfrey in 'Selma' - also said she loves working with the TV chat show host and her ''good friend''.

She said: ''She's a good friend of mine. I like working with her, she's a really strong actor.

''You forget that with all the other stuff going on. The other day she sold some stock and made $110m!''