Her students, all boys, were a range of ages, and thus the class was called "ungraded". Soon other "ungraded" classes were established in New York schools, after her model; in 1906 Farrell became director of special education, with the title "Inspector of Ungraded Classes."
As Inspector, Farrell began a diagnostic clinic to test schoolchildren for underlying causes of poor academic achievement. She also began a journal, titled Ungraded, to share findings with other special education professionals. She was a frequent lecturer, and taught pioneering special education courses at Teachers College Columbia University and at the University of Pennsylvania.