He also served as chairman of the department from 1959 to 1962 and became professor emeritus of psychology in 1964, the same year he retired from the university. In 1963 Keller was invited to Brazil to São Paulo to incorporate his new psychology into their existing academics. Keller returned to the U.S. and was invited back to Brazil, this time to the University of Brazila, where he was instructed to continue the development of his new findings. Upon returning for good, Keller found employment at the Institute for Behavioral Research, as well as Western Michigan University, Texas Christian University, and Georgetown University. Keller spent his time as a visiting professor, adjunct professor, as well as the chair at the listed universities. He retired in May 1976 from Georgetown University. Keller's students appreciated him as their instructor, as well as appreciated his frequent reinforcers of their behavior. His "theoretical commitment to the power of positive reinforcement… he delivered were never routine" but "mechanical repetitions of 'uhhunh' or 'good. It was seen as a possible plan to increase academic performance and often singled out his students to denote praise. He was recognized throughout his life and was liked by many. After his death, a memorial was held in San Francisco by the Association for Behavior Analysis, in which over two hundred people took part in. Keller was also recognized for his "effects of his lectures on one student's behavior ... efficacy of his teaching" and "graceful flow of sentence into paragraph". Inspired by B. F. Skinner, Keller proposed a reinforcement theory that applies to his teaching in addition to research. He and William N. Schoenfeld produced a textbook as well as an introductory laboratory course in psychology that related animal psychology with white rats as their subjects. The textbook was called "Principles of Psychology," published in 1950. The book emphasized scientific methods in the study of psychology such as escape, avoidance, conflict, cooperation, imitation, verbal behavior, thinking, and concept formation. In addition to providing a course that initiated the first use of experimental analysis of behavior during his time at Columbia University, Keller and Schoenfeld provided a more concise understanding for concepts that Skinner proposed in his "The Behavior of Organisms". Concepts were written in a clearer way for students to understand and was more appropriate for an undergraduate beginners course. In the lab, students were able to test the methods they were learning of in their lecture classes for the first time. Among their experiments, the students observed the responses of white rats to stimuli and rewards and measured human learning by testing people's ability to remember the pathways of mazes and other sensory processes.