Within the last ten years Doignon and Falmagne's knowledge structures
theory has become well-known in knowledge psychology. With the aim of
modeling a certain domain of knowledge in the area of elementary geome
try, this paper discusses critically the theory of knowledge structure
s. An extension of this theoretical approach is proposed, in which ''k
nowledge'' is modeled as competence and performance. Performance refer
s to the observable behavior in solving the given problems, whereas co
mpetence is conceived as a not directly observable theoretical constru
ct (interpreted as ''ability'', ''skill'' or ''knowledge'') for the de
scription, explanation, and prognosis of the observable solution behav
ior. The connection between competence and performance is formally spe
cified on the basis of deterministic test-theoretical assumptions. The
competence-performance conception is illustrated by modeling a knowle
dge domain within the area of the geometry of right triangles. Results
from an empirical validation study are reported and analyzed. Finally
, the advantages and disadvantages of the proposed competence-performa
nce conception of the knowledge structures theory are discussed.