Anne Bancroft won the Oscar for playing Annie Sullivan in The Miracle Worker.
The Miracle Worker is a fantastic film that doesn't feel stagy or slow - it's almost a miracle because most stage plays fail on the big screen. I think what makes the film work so much is how much of a "movie" it is, the scenes pop and the performances are largely physical. The story of how Helen Keller was able to learn how to function as a person, all thanks to a determined and strong willed teacher, Annie Sullivan.
Anne Bancroft never once lets Patty Duke overshadow her, they both work wonders together, and their chemistry on screen made for some intense and realistic fight scenes. While the performance of Patty Duke is much more interesting, it's Anne Bancroft's performance where we see true emotional vulnerability. She is haunted by her past and when she describes incidents in her past, Bancroft invests so much into these scenes, it's unbelievable how hard she is acting, when she had already played this character many times on the screen.
She is amazing at how much she does and when the camera really takes notice of her, she sells the character of Annie for everything she is worth.