The questionnaire responses of 38 secondary school mathematics teachers provided initial data for this study. About 26.3% (n = 10) of this number was sampled for classroom observation and in-depth interviews in order to assess the consistency of the dispositions. Only 15.8% of the schools in the study adopted the calculator version of the "O" Level curriculum, 4028. The teachers' dispositions showed competence to use scientific calculators during instruction but maintained teacher-centred instructional approaches in both classrooms where students possess calculators and logarithms. This finding raises fears that even when calculators are available, they may remain on the periphery of mathematics instruction when they continue to be narrowly used as computational devices. Implications of these results are explored with a goal of providing teachers with insight into how to use calculators effectively in the "O" Level mathematics curriculum.