Head Masters challenges the assumption that phrenology—the study of the conformation of the skull as it relates to mental faculties and character—played only a minor and somewhat anecdotal role in the development of education. Stephen Tomlinson asserts instead that phrenology was a scientifically respectable theory of human nature, perhaps the first solid physiological psychology. He shows that the first phrenologists were among the most prominent scientists and intellectuals of their day, and that the concept was eagerly embraced by leading members of the New England medical community.

Following its progression from European theorists Franz-Joseph Gall, Johan Gasper Spurzheim, and George Combe to Americans Horace Mann and Samuel Gridley Howe, Tomlinson traces the origins of phrenological theory and examines how its basic principles of human classification, inheritance, and development provided a foundation for the progressive practices advocated by middle-class reformers such as Combe and Mann. He also elucidates the ways in which class, race, and gender stereotypes permeated 19th century thought and how popular views of nature, mind, and society supported a secular curriculum favouring the use of disciplinary practices based on physiology.

This study ultimately offers a reconsideration of the ideas and theories that motivated education reformers such as Mann and Howe, and a reassessment of Combe, who, though hardly known by contemporary scholars, emerges as one of the most important and influential educators of the 19th century.