Geary received a BS degree in psychology from Santa Clara University (California) in 1979, and an MS from the clinical child/school psychology program at California State University at Hayward (now East Bay) in 1981. After completing the MS degree, he worked for the emergency treatment center of the Mental Research Institute in Palo Alto, California, and began the Ph.D. program at the University of California, Riverside, in 1982. His initial interests were in hemispheric laterality and associated sex differences, but focused his dissertation work on mathematical cognition under the direction of Keith Widaman (now at UC, Davis). After completing his Ph.D. in developmental psychology in 1986, he took a one-year position at the University of Texas at El Paso and then moved to the University of Missouri, first at the Rolla campus (1987–89) and then in Columbia. During this time, he served as chair of the Department of Psychological Sciences (2002–2005) and contributed heavily to the creation of the Ph.D. program in developmental psychology.