Sidney L. Pressey (Brooklyn, New York, 1888  1979) was Professor of Psychology at Ohio State University for many years. He is famous for having invented a teaching machine many years before the idea became popular.

"The first.. [teaching machine] was developed by Sidney L. Pressey... While originally developed as a self-scoring machine... [it] demonstrated its ability to actually teach".

Career 
Pressey joined Ohio State in 1921, and stayed there until he retired in 1959. He continued publishing after retirement, with 18 papers between 1959 and 1967. He was  a cognitive psychologist who "rejected a view of learning as an accumulation of responses governed by environmental stimuli in favor of one governed by meaning, intention, and purpose". In fact, he had been a cognitive psychologist his entire life, well before the "mythical birthday of the cognitive revolution in psychology".

Pressey was the first winner of the E.L. Thorndike Award for achievements in educational technology, in 1964. This is an award of the American Psychological Association.

Early readability formula 
In 1923, Pressey and a co-worker published the first reading ease formula. They had been concerned that science textbooks in junior high school had so many technical words. They felt that teachers spent all class time explaining their meaning. They argued that their formula would help to measure and reduce the “vocabulary burden” of textbooks. Their formula, based on the Thorndike word list, took three hours to apply to a single book. It was a measure of vocabulary difficulty. Many later formulae made use of some measure of sentence complexity as well as vocabulary. These are the two main causes of text difficulty or 'readability'.

The 'teaching machine' 
Pressey's idea started as a machine for administering multiple-choice questions to students. These were (and are still) a basic method for testing students in the U.S.A.. The machine had a window with a question and four answers. The student pressed the key  to the chosen answer. The machine recorded the answer on a counter to the back of the machine, and showed the next question.

The great idea was to fix the machine so that it would not move on until the student chose the right answer. Then it was easy to show that the second arrangement taught the students what were the right answers. This was the first demonstration that a machine could teach, and also a demonstration that knowledge of results was the cause of the learning.

A number of reviews credit Pressey with being the founder of programmed learning and teaching machines, long before the better known efforts of B.F. Skinner. Skinner was, however, responsible for bringing the whole subject into popular view, and his critique of the limitations of traditional classroom teaching is a classic work.

Works 
Pressey S.L. & Pressey L.C. 1923. Introduction to the use of standard tests. Harrap.
Pressey S.L. & Pressey L.C. 1927. Mental abnormality and deficiency. Macmillan. 
Pressey S.L. 1933. Psychology and the new education. Harper.
Pressey S.L. & Robinson F.P. 1944. Psychology and the new education. Revised edition, Harper.
Pressey S.L. & Janney J.E. 1937. Casebook of research in education. Harper.
Pressey S.L; Janney J.E. & Kuhlen R.G. 1939. Life: a psychological survey. Harper.
Pressey S.L. & Kuhlen R.G. 1957. Psychological development through the life span. Harper & Row.. 
Pressey S.L; Robinson F.P & Horrocks J.E. 1959. Psychology in education. Harper.

Autobiographies 
Pressey, Sidney L. 1967. Autobiography. In A history of psychology in autobiography, vol 5. eds Edward G. Boring and Gardner Lindzey. New York: Appleton-Century-Croft.
Pressey, Sidney L. 1971. Sidney Leavitt Pressey, Part I: An autobiography. In Leaders in American education, ed. Robert J. Havighurst. Chicago: University of Chicago Press.

References 

1888 births
1979 deaths
Educators
American psychologists