This study examined the effects of an integrated mathematics and science curriculum with life-skills applications on academic achievement in a Saudi Arabian elementary school. An integrated unit was developed covering the grade 5 ‘sound and light’ science unit and the ‘perimeter, area, and size’ mathematics unit, using practical applications activities connected to the students’ everyday lives. The study involved treatment (n = 36) and comparison (n = 41) groups of grade 5 students (females) enrolled in a private school in Dhahran City. The comparison group was instructed using a conventional approach involving separate science and mathematics units, while the treatment group was instructed using the integrated unit. Two achievement tests for the target science and mathematics units were developed and used in the pretest-posttest design to verify the equivalence of the treatment and comparison groups before conducting the study, and to compare the achievement results after implementing the conventional and treatment units. The study found statistically significant differences favouring the treatment group on the achievement posttest (effect sizes were 0.44 for science and 0.49 for mathematics). These large effect sizes indicated the positive impact of using the proposed strategy of curriculum integration to evaluate the teaching program to see if the goal of improved achievement was actually realised.