The study examined the impact of concept-based instruction on the teaching and learning of mathematics. Functions is the topic that was implemented in order to identify the improvements in learners' understanding. A total of 35 Grade 11 learners from a South African township school in Limpopo province participated in this study. Data were collected using tests, questionnaires, and semi-structured interviews. The constructivist learning theory underpinned the exploration. All the 35 participants wrote a test twice, completed a questionnaire and only 6 of them were interviewed. The study employed the sequential explanatory research design because of its richness in data findings as it incorporates both quantitative and qualitative research methods. The initial stages of data analysis started with emerging themes from data being coded and categorised. To identify changes in learners' performance in the administered pre and post assessment tests, a dependent t-test was carried out, while questionnaires and interviews were used to assess learners' attitudes and perceptions. The findings from the inquiry indicated positive gains in deep understanding, critical thinking, long-term retention of information, transferable skills, engagement and integration, which are all directly linked to conceptual understanding, resulting in enhanced performance. Both numerical and descriptive analyses confirmed that concept-based instruction enables learners to construct their own knowledge and enhance their conceptual understanding which in the end improves their performance in mathematics. The findings confirm that learners responded positively to concept-based instruction and suggest its broad adoption in mathematics education to address issues of conceptual gaps. Contribution: The study provides teachers with an opportunity to implement innovative teaching and learning approaches such as the concept-based instruction to improve learners' conceptual understanding.