This empirical study investigates the impact of metacognitive strategies and self-regulating processes in learners' achievement on solving math word problems. It specifically analyzes the impact of the linguistic factor and the number of steps and arithmetical operations that learners need to apply during the process of solving math word problems. Two hundred sixty-three learners, of three classes of third graders (N=130) and four classes of fifth graders (N=133) of the elementary cycle from two urban schools of Kosovo, participated in the study. Almost half of the total number of the third and fifth-graders were exposed to metacognitive instruction. The rest of the learners were included in control classes in which they performed tasks without having been given any specific guidance, based exclusively on traditional methods and respective textbooks. All the learners were tested in math word problems twice, before the intervention and after it. Research findings have shown that metacognitive strategies and self-regulating processes that learners use to control their actions, to reason, and to reflect, are one of the main resources that influence their success in solving a math word problem. Although the difference between the pre-test and the post-test results was statistically significant solely with the fifth-grade experimental classes, yet an improved performance was observed in third-grade experimental learners' classes compared to control classes. Theoretical and practical implications of the research are discussed in the end of the study.