Minimal guidance or maximal independence? How can teachers achieve that complex balance when teaching mathematics? In this pre-and post-test quasi-experimental research study, the authors explored the above broad questions in Grade 10 Financial Mathematics following guided discovery and mathematical modelling principles. Fifty-four (54) Grade 10 students at a Government High School in Johannesburg, South Africa, participated in the study. One group of students was taught following guided discovery and modelling principles and another group was taught the same contents but following explicit instruction. Students' mean scores were compared at the end of the interventions. Two teachers with similar experience and qualifications taught the two groups independently. The main findings revealed that although the overall performance in the posttest appeared similar in both groups, there was in fact a significant difference in understanding the concept of compound interest in the guided discovery and modelling group compared with the explicit instruction group. The research highlights the promise offered by the former teaching approaches over explicit instruction in supporting the understanding of difficult concepts to the students. Our findings led us to propose that foundation skills such as, plotting coordinate points, reading, and interpreting graphs, substituting into, and using formulas, and factorizing algebraic expressions should be thoroughly covered at the lower high school to prepare students to cope with more challenging related concepts at the higher level.