It is hypothesized that certain mental structures are related to certain teaching skills. These structures are identified as combinatorial logic, essential to planning lessons, and hypothetical reasoning, an important aid in analyzing lessons. These formal thinking abilities should result in greater improvement during practice and later teaching. It was assumed in testing this hypothesis that there is a relationship between three teaching competencies--planning lessons, analyzing lessons, and manipulation of concrete and abstract ideas to derive generalizations that may be used to improve teaching--and the cognitive style of the teacher. Teacher education students were assessed in individual interviews for formal thinking abilities. Tests consisted of Piaget's colorless liquids, stickman, and conservation of motion tasks, and a paper and pencil test of formal reasoning. Reliability of teaching ability rankings was checked by supervisors who ranked the student over a period of four months. Results of this research did not support the hypotheses that related lesson planning to combinatorial logic and overall teaching effectiveness to formal thinking. Data supported the hypothesized relationship between the ability to analyze lessons and hypothetical reasoning. Samples of the tests used are appended to this report. (JD)