TPR Storytelling is based on two key theoretical pillars: the input hypothesis, and mastery learning.
Input hypothesis
The Input Hypothesis, proposed by Dr. Stephen Krashen, suggests that language development is a function of the input received by the learner. Krashen asserts that there are two distinct ways of learning language: language "learning" and language "acquisition". Language "learning" is learning that takes conscious effort on the part of the learner. It is characterized by learning grammar rules, memorizing vocabulary lists, and performing speaking drills. Language "acquisition" is learning that is subconscious and takes little or no effort on the part of the learner. It is characterized by listening and understanding to messages, reading interesting books and articles, and other enjoyable activities that take place in the language being learned. According to Krashen's theory, the only thing that can lead to fluency in the language is language "acquisition". Language "learning" can only be used as a way to consciously edit speech or writing, and it is never the cause of spontaneous, unrehearsed speech or writing.
In light of this theory, TPRS teachers spend the vast majority of their class time on input-based activities. In the table below, you can see the different activities used in TPR Storytelling, and whether they encourage language learning, language acquisition, or both. The activities that include a language learning component all take up a relatively short amount of class time. On the other hand, the pure acquisition activities take up large amounts of time. For typical TPRS classes, the ratio works out at about 5% of time spent on learning and 95% of time spent on acquisition.
The affective filter
Another key component of Krashen's theory is the affective filter. The affective filter hypothesis states that language is more easily acquired when people are relaxed and open to learning. On the other hand, if people are experiencing negative emotions such as anxiety, self-doubt, and boredom, language is a lot less likely to be acquired.
For this reason TPRS teachers always try to make students look good in the stories and discussions. For example, an otherwise average student could be given the role of a star baseball pitcher in a class story. It is usually considered good form to make celebrities look bad in comparison to the students. The class story in question might see the pitcher winning a game against an all-star team of professional batters, ideally in a humorous way. This use of humor and making the students look good is all built on the idea that students learn language better when they are enjoying themselves.
Mastery learning
Mastery learning is a method of instruction in which students thoroughly learn all material they are studying. Students do not progress on to learning new material until they have mastered current material. This gives students a feeling of control, and indeed, of mastery. In language learning this is particularly important, as this feeling of control is directly related to the ability to learn. This is demonstrated by Krashen's research on the "affective filter".
The mastery approach to learning manifests itself in TPR Storytelling in many ways. Firstly, the number of new vocabulary phrases to be learned in each lesson is usually not more than three. More words than this may be introduced during the lesson, but the three phrases are the only ones that the students will be expected to know. Secondly, these vocabulary phrases are repeated many, many times, in context, using the "circling" technique. This repetition helps the students to internalize the words thoroughly. In addition, the same words are used during the class reading, giving even more repetition. If after this, the students still aren't comfortable with the target words, the teacher can simply tell a new story using the same vocabulary phrases in the next lesson. Thirdly, teachers will try as far as possible to review all previously covered vocabulary in every lesson, finding ways to work the old vocabulary structures into class stories and class discussions.