Lesson starts are transitional events which may cause management problems for teachers. This study sought junior secondary school mathematics teachers' beliefs about calculator use in mathematics instruction in Botswana and was descriptive in nature adopting a survey design. The sample of seventeen (17) mathematics teachers from four (4) junior secondary schools in the Tutume Sub-district in Central Educational Region was selected through a purposive random sampling procedure. A questionnaire comprising both closed and open ended questions was designed to collect data then the analysis of results was carried out using descriptive and inferential statistics. As an illustration, a t-test was used to test for differences in teachers' beliefs by gender while a one-way ANOVA was used to test for difference in their beliefs by experience. The study revealed that most of the teachers expressed their lack of confidence and were incompetent with the use of a calculator in their teaching with female teachers feeling less confident to explain different functions of a calculator than their male counterparts. In addition, the study showed that most of the teachers believed that a calculator was a technological tool that could be useful to the students in the future. On the contrary, most teachers felt that the overuse of calculators by the students could hamper the development of basic computational skills. Therefore, it was recommended that school based training on calculator use should be provided so as to empower teachers with the necessary technological skills for effective classroom instruction. The study findings have implications to research and practice as it provides unique and comprehensive data that will lead to insight for curriculum designers, policy implementers and instructional leaders on effective calculator use in math instruction.