Written materials—The primary presentation of new content should be through written texts. Given the forms of media available at the time when the Keller Plan was developed (e.g., lectures, movies, audio records, television, radio, paper-based text, etc.), paper-based texts gave students the greatest freedom; books and texts are portable, can be read at one's own pace, can be started and stopped at any time, can be easily reviewed, and can be marked by the reader. As an application of behaviorism, the Keller Plan was meant to maximize the number of operant behaviors that could be reinforced; this could best be done with written materials rather than have the learner be a passive observer of other media. Digital media available today could  provide the same kinds of learner control and presumably could be incorporated in a contemporary implementation of PSI  . Units of content—Subject matter material should be broken down into separable, meaningful units. These units could have various kinds of relationships; for example, one could provide prerequisites for understanding a second, or the second could provide deeper elaboration of a proceeding unit. In any case, specific learning objectives should be definable for each discrete unit of content. Self-paced instruction—Students should be allowed to advance through the course material at their own pace. While an instructor might specify the order in which learning units are completed, the learners should decide when and at what rate they learn. Learners could move through a course as quickly or slowly as they choose. Unit mastery—Students must satisfy a mastery requirement in one unit before proceeding to the next. Typically, a unit in PSI would have more than one equivalent form of assessment—for example, three quizzes of equal difficulty or three primary sources or data sets to be analyzed. Students must demonstrate mastery of a unit's objectives to a certain level of quality. If the student does not reach the threshold, they are redirected to unit materials (or supplements if provided) and then take an equivalent form of the unit assessment. From the point of view of behaviorism, demonstrating mastery and being allowed to continue to a subsequent unit was presumed to be reinforcing Proctors—Human proctors are an important part of the Keller Plan. The proctors could be "external" to the course (adults or peers brought to the course from external sources) or "internal" (advanced students in the course who are doing well, have completed all units to date, and have good interpersonal skills). Proctors were the arbiters of unit mastery; they would "certify" mastery, discuss areas of weakness, and direct students to the next units. Behaviorists were always concerned about bringing conditioned behaviors under the control of "natural" reinforcers; interactions with the proctors were presumed to provide natural social reinforcers that encouraged learning behaviors and perseverance in the course.
Written materials—The primary presentation of new content should be through written texts. Given the forms of media available at the time when the Keller Plan was developed (e.g., lectures, movies, audio records, television, radio, paper-based text, etc.), paper-based texts gave students the greatest freedom; books and texts are portable, can be read at one's own pace, can be started and stopped at any time, can be easily reviewed, and can be marked by the reader. As an application of behaviorism, the Keller Plan was meant to maximize the number of operant behaviors that could be reinforced; this could best be done with written materials rather than have the learner be a passive observer of other media. Digital media available today could not provide the same kinds of learner control . Presumably, unintended consequences might arise if incorporated into a contemporary implementation of PSI , due to many additional operant behaviors that cannot be controlled by the student or teacher . Units of content—Subject matter material should be broken down into separable, meaningful units. These units could have various kinds of relationships; for example, one could provide prerequisites for understanding a second, or the second could provide deeper elaboration of a proceeding unit. In any case, specific learning objectives should be definable for each discrete unit of content. Self-paced instruction—Students should be allowed to advance through the course material at their own pace. While an instructor might specify the order in which learning units are completed, the learners should decide when and at what rate they learn. Learners could move through a course as quickly or slowly as they choose. Unit mastery—Students must satisfy a mastery requirement in one unit before proceeding to the next. Typically, a unit in PSI would have more than one equivalent form of assessment—for example, three quizzes of equal difficulty or three primary sources or data sets to be analyzed. Students must demonstrate mastery of a unit's objectives to a certain level of quality. If the student does not reach the threshold, they are redirected to unit materials (or supplements if provided) and then take an equivalent form of the unit assessment. From the point of view of behaviorism, demonstrating mastery and being allowed to continue to a subsequent unit was presumed to be reinforcing Proctors—Human proctors are an important part of the Keller Plan. The proctors could be "external" to the course (adults or peers brought to the course from external sources) or "internal" (advanced students in the course who are doing well, have completed all units to date, and have good interpersonal skills). Proctors were the arbiters of unit mastery; they would "certify" mastery, discuss areas of weakness, and direct students to the next units. Behaviorists were always concerned about bringing conditioned behaviors under the control of "natural" reinforcers; interactions with the proctors were presumed to provide natural social reinforcers that encouraged learning behaviors and perseverance in the course.
A
not
R
and presumably could be incorporated in
. Presumably, unintended consequences might arise if incorporated into
A
, due to many additional operant behaviors that cannot be controlled by the student or teacher