To make it easier for students to learn the contents of physics and increase their motivation to learn, physics teachers need to apply different teaching strategies. With this study we aimed to examine the impact of the modified Know-Want-Learn (mKWL) strategy in physics teaching on elementary school students' metacognition. The pedagogical experiment with parallel groups was applied to determine whether the mKWL strategy affected students' metacognition. The students in the experimental group were taught by applying the mKWL strategy with a specific chart. The chart consisted of columns: T -- What I think and what I know, Q -- What questions I have, H -- How can I find out, L -- What I Learned (TQHL chart). The students in the control group were taught (the same physics curriculum) by using the traditional teaching model, without this TQHL chart. A questionnaire on metacognition was used for the evaluation of sixth-grade students' metacognition. The statistical analysis of data included descriptive statistics, as well as paired sample t-tests and independent sample t-tests. Research results, based on the scores obtained using the questionnaire on metacognition, imply that the use of the proposed mKWL strategy increases students' metacognition. Considering the positive effect of this teaching strategy on students' metacognition, its further application in other teaching subjects is planned as well as the training of a large number of elementary school teachers for its application.