This research examined the competencies (preparedness, skills, knowledge and self-efficacy beliefs) of High School teachers in teaching mathematics with technology. The study employed the explanatory sequential mixed-methods design where a questionnaire, observation guide and semi-structured interview guide were used to collect data. A stratified sampling technique was used to select 202 mathematics teachers for the study. Descriptive statistics and multiple regression were employed to analyse the quantitative data. Thematic analysis was used for the qualitative data. The findings indicated that mathematics teachers possessed high technology knowledge and self-efficacy, but they had relatively low preparedness and ICT skills in using technology in their lessons. In addition, ICT skills and teacher preparedness emerged as the best predictors for technology usage in mathematics lesson delivery. This implies that mathematics teacher education programmes should consider making ICT a core component of their curriculum to prepare prospective teachers to teach mathematics with technology.