Surveying the scene at the turn of the last century, Abraham Flexner was repelled by the lax or nonexistent standards at American proprietary medical schools.

In his 1910 report, "Medical Education in the United States and Canada: A Report to the Carnegie Foundation for the Advancement of Teaching," he urged the elimination of for-profit medical schools. Following the Flexner report, many medical schools merged or were closed outright.

He helped establish standards for pre-requisite education, framed medical school admission criteria, aided in the design of a curriculum introduced by the basic sciences and followed by the clinical sciences, stipulated the resources necessary for medical education including government funding, and emphasized medical school affiliation with both a university and a strong clinical system.

He hastened the standardization of medical education and recommended the adoption of standards established by the AMA's Council on Medical Education in 1904: four years of medical school consisting of two years of didactic training followed by two years of clinical rotations.

Kenneth Ludmerer, M.D., a professor of medicine at Washington University School of Medicine, in an essay on Flexner's legacy in the February Academic Medicine, noted that Flexner laid the groundwork for the elements of modern medical education: medical positivism—meaning that medicine was governed by general, reproducible laws of biology; rigorous entrance requirements; original research guided by the scientific method; and "learning by doing."

"Flexner espoused a model system of medical education in which all schools were to be of the same kind—university-based, research-oriented schools.... Only the most uncompromisingly academic model for a medical school was acceptable to him. There was no room in his system for ‘practical,’ non-research-based schools, even if they happened to provide respectable teaching. This is precisely the system that was ultimately created, and medical schools soon became much more homogeneous than before."