In the early 1940s, based on his research in behavior, he developed a new technique for teaching Morse Code to military personnel that the U.S. Army Signal Corps adopted officially in 1943. Keller was a Harvard classmate and lifelong friend of the behaviorial psychologist B. F. Skinner and was, with him, among the first American proponents of behaviorism, which emphasizes the role of environmental events in the shaping of human behavior. In 1947 Keller, with his colleague William Schoenfeld, instituted at Columbia College the first undergraduate psychology course to use Skinner's experimental methods. Students taught white laboratory rats to respond to stimuli through rewards. The point of the experiments was to demonstrate the idea that broad principles of behavior could be discovered experimentally, and that such principles had important applications to human society.
Many colleges now offer courses in experimental psychology using laboratory animals.
Behavior theory held tremendous potential to help educate people better, the two authors believed. Rather than dictating long bursts of code to students, instructors using his method told students after each signal whether they had correctly decoded it. That approach gave students instant feedback, allowed them to correct mistakes immediately and was far more effective in teaching the code than previous methods. In 1948 Keller received the Certificate of Merit from President Truman for the Morse Code work, and he used the method to teach the code to Columbia College undergraduates preparing for military service. After retiring from Columbia in 1964, Keller went to the University of Brasilia in Brazil, where he helped found the psychology department and offered the first course using his personalized instruction method.