The relevance of the concept of culture to school effectiveness and sc
hool improvement is explored. Two typologies are developed. The first
proposes four 'ideal type' school cultures, based on two underlying do
mains; the second, a more elaborate and dynamic model, proposes two 'i
deal type' school cultures, based on five underlying structures. Each
is discussed for its heuristic, conceptual, methodological and explana
tory potential in research in the fields of school effectiveness and s
chool improvement. In distinguishing collegial cultures from collabora
tive styles, the article advances recent writing on collaboration. Fro
m the theory hypotheses about the relationship between school culture
and school effectiveness and improvement can be derived as well as tec
hniques to test such hypotheses.