The interest in school ergonomic intervention programs and their effects on musculoskeletal pain is increasing around the world. The objective of this longitudinal randomized control trial was to implement and measure the effects of a computer-related ergonomics intervention on grade eight learners in a school environment in Johannesburg South Africa (a developing country). The sample comprised of a control group (n= 66) and an intervention group (n= 61). The outcome measures used were posture assessment using the Rapid Upper Limb Assessment tool (RULA) and the prevalence of musculoskeletal pain using a visual analogue scale (VAS). Measurements were done at baseline, three months and six months post intervention. The results showed that the posture of the intervention group changed significantly from an Action Level 4 to an Action level 2 and Action level 3, indicating a sustained improvement of learners' postural positions whilst using computers. The intervention group showed a significant reduction in the prevalence of musculoskeletal pain from 42.6% at baseline to 18% six months post intervention (p< 0.003). In conclusion, the results indicated that a computer-related intervention program for grade eight learners in a school environment is effective and that behavioural changes can be made that are sustainable over a period of six months.