This investigation addressed the following questions: (1) Can the ability to control variables be taught to high school biology students who, on a written test of logical operations, do not demonstrate formal reasoning; (2) Would students who are classified as early formal operational thinkers on the written test of logical operations be able to benefit more from the training than students who are classified as early or late concrete operational thinkers; and (3) If the ability to control variables can be learned, is it generalizable to problems utilizing novel materials? Sixty-five high school students (29 males and 36 females) enrolled in a biology course at Delphi High School in Delphi, Indiana, served as subjects. This research found that training was not successful in promoting appreciable understanding of the controlling variables concept. Also found was that understanding of the concept of controlling variables is lacking and not easily corrected. The training of specific Piagetian concepts was successful, but the students did not exhibit transfer of the training. (Author/DS)