Information about good practice in classroom teaching is needed to inform educational planners and practitioners of the development and improvement of curricula and teaching and as a resource for further curriculum reform. This paper, part of a study on teacher effectiveness, reports on classroom research in a Malaysian secondary school 4 years after the implementation of the Integrated Secondary School Curriculum (ISSC), a planned educational innovation. The practices of 16 secondary school mathematics teachers were identified as effective through systematic classroom observations. Findings indicate there exists little evidence, even from the practice of effective teachers themselves, to support the claims about the practices of effective teachers as prescribed by the ISSC, although retraining of teachers had taken place prior to implementation of the curriculum. Since teachers develop their own sustainable approach towards good practice, it was argued that effort had to be made to reduce the mismatch between what ought to be prescribed by the curriculum and what ought to be practiced by the teachers, particularly on how beliefs about good practices should be developed and then carried out effectively by the teachers in the classroom. (Contains 28 references.) (LL)