This study combined the principles of multimedia message design with an enclosing-rectangle scaffold to facilitate instruction on deriving the area of basic geometric shapes. A pretest/posttest/delayed-posttest design was used to compare the effectiveness of the enclosing-rectangle scaffold with that of conventional dissection/rearrangement methods among low-achieving seventh-grade students. These fifty-six low-achieving students were averagely assigned to one of two teaching methods. In immediate and delayed testing, an enclosing-rectangle scaffold proved significantly more effective than the conventional approach (posttest: F (1,53) = 16.148, p = <0.001, [eta][superscript 2] = 0.234; delayed posttest: F (1,53) = 13.502, p = <0.001, [eta] [superscript 2] = 0.203). These findings demonstrate the effectiveness of stepwise visualisation within a coherent context in facilitating the selection, organisation, and integration of mathematical concepts. Given the ongoing challenges that students face in comprehending the formula for calculating the area of a trapezoid, there is a need for further research in this area to identify effective instructional approaches and strategies.