Teaching high school students and college freshmen to construct dichotomous keys for the identification of plant or animal species is often one of the most difficult and challenging tasks an instructor has to face. Students often have had limited exposure to this type of keys, and have not experienced the types of difficulties which the user of a poorly constructed key is likely to face. Students' first attempts at construction of keys are apt to fall short of the mark in several respects: first , the keys often utilize comparative terms like "big" or "small;" second, they frequently contain ambiguous or poorly defined qualifiers, or qualifiers failing to give proper contrast between opposing legs of the key; and third, many students fail to grasp the dichotomous nature of the standard key format. Even graduate students have been known to err along these same lines.
dichotomous keys, teaching methods