The O-School, formally the Sonia Shankman Orthogenic School, is a therapeutic day school in Chicago, Illinois. It serves elementary, middle, and high school students who need intensive educational and therapeutic support, and it is known historically for its association with milieu therapy and the University of Chicago.

The school traces its origins to 1915 and became widely associated with Bruno Bettelheim, who directed the Orthogenic School from 1944 to 1973. The school's own history describes Bettelheim's tenure as central to the development of its milieu-therapy approach, while noting that later directors Jacqui Sanders and Bertram Cohler carried the model forward.

In 2014, the O-School separated from the University of Chicago and moved into a custom facility in Chicago's Woodlawn community, a few blocks south of the university campus. The school later reorganized around an expanded day-school model. Its current programs include the therapeutic day school, a Transition Learning Center, Camp O, and a Diagnostic and Evaluation Center.

The O-School states that it is accredited or reviewed by Cognia and the Illinois State Board of Education and lists organizational affiliations with the Association of Children's Residential & Community Services, the Illinois Association of Private Special Education Centers, the National Association of Private Special Education Centers, and the National Association of Therapeutic Schools and Programs. Public source material includes the school's therapeutic day school, history, and accreditation pages.