Purpose: This study aims to investigate the development of Mathematics teachers' attitudes towards technology integration through collaborative lesson design activities as part of professional development. Design/methodology/approach: The pre-and post-test for non-equivalent comparison groups quasi-experiment was adopted as the study design where 125 participants were distributed into three groups in Dar es Salaam -- Tanzania. Data analysis was done using gain in scores, t-test, split-plot analysis of variance, and eta-squared. Findings: Comparison across groups and between pre-intervention and post-intervention showed that collaborative lesson design activities have more potential to develop Mathematics teachers' attitudes than the isolated implementation of such activities. Relevant recommendations are provided. Practical implications: The study offers valuable insights for teacher education especially in-service training focussing on effective ways of developing teachers' competencies especially attitudes towards technology integration. Originality/value: Although lesson design studies are prevalent, majority have investigated the development of teachers' knowledge rather than attitude for integrating technology. Additionally, the study sheds light on attitude as a multidimensional construct thereby providing more insight into the subject.