South Africa has a unique cultural, historical, socio-economic and linguistic contextual complexity that influences the implementation the intended curriculum and educational policies. The contextual complexity continues to result in Science teachers entering into the teaching profession with a wide spread diversity in background and qualifications. The secondary data analysis used a concurrent mixed methods approach (QUAL + quan) to explore the interconnection between teacher characteristics, classroom practices and learner achievement in Physical Science. The primary sample consisted of 18 schools that were stratified by district and quintile. From the available data, nineteen Grade 12 Physical Science teachers with varying levels of qualifications and experience were analysed. A combination of qualitative and quantitative instruments, specifically, Science teacher questionnaires, Science lesson observations and Science teacher interviews, were explored. The data was analysed quantitatively using descriptive statistics, frequency tables and Pearson correlation coefficients. The qualitative data involved content analysis and the presentation of case studies and the themes that emerged. Significant Pearson correlations indicate a positive relationship between years of related experience and pass rates and also pointed to an interconnection between professional qualifications, related experience and learner achievement. Differences in teacher characteristics were also indicators of competency in content knowledge and ultimately influenced classroom practices. Four case studies are offered in an attempt to provide in-depth descriptions of the teacher characteristics and practices for Grade 12 Physical Science teachers in Gauteng. Recommendations for future research, teacher training and policy implementation are presented. The diversity in teacher characteristics, particularly in Physical Science classrooms, influences the classroom practices that teachers select in their day-to-day teaching and impacts learner outcomes in terms of achievement.