From the view of schema-transfer theory, the use of schemata with their several functions gives an explanation for the facilitative effect of prior knowledge on learning processes. This report gives a theoretical exploration of the concept of schemata, underlying schema theories, and functions of schemata to indicate the importance of schema theories in the context of an ongoing research project on prior knowledge state. A schema is a fundamental element on which all information processing depends, a data structure for representing generic concepts stored in memory. Embedded in the unit in addition to the knowledge itself is information about how the knowledge is to be used. The prior knowledge state has a central role in all schema theories. The starting point for constructing a representation is what the learner already knows. It seems obvious that the student's schemata or knowledge structures will give concrete information about their prior knowledge state. Seven figures illustrate the discussion. (Contains 87 references.) (SLD)