Background: Enhancing students' metacognitive abilities will help to facilitate their understanding of science concepts. Purpose: The study was designed to conduct and evaluate the effectiveness of a repertoire of interventions aimed at enhancing secondary school students' metacognitive capabilities and their achievements in science. Sample: A class of 35 Year 9 students participated in the study. Design and methods: The study involved a pre-post design, conducted by the first author as part of the regular designated science programme in a class taught by him. In order to enhance the students' metacognitive capabilities, the first author employed clearly stated focused outcomes, engaging them in collaborative group work, reading scientific texts and using concept mapping techniques during classroom instruction. The data to evaluate the effectiveness of the metacognitive interventions were obtained from pre- and post-test results of two metacognitive questionnaires, the "Metacognitive Support Questionnaire" ("MSpQ") and the "Metacognitive Strategies Questionnaire" ("MStQ"), and data from interviews. In addition, pre-test and post-test scores were used from a two-tier multiple-choice test on Light. Results: The results showed gains in the "MSpQ" but not in the "MStQ." However, the qualitative data from interviews suggested high metacognitive capabilities amongst the high- and average-achieving students at the end of the study. Students gains were also evident from the test scores in the Light test. Conclusion: Although the quantitative data obtained from the "Metacognitive Strategies Questionnaire" did not show significant gains in the students' metacognitive strategies, the qualitative data from interviews suggested positive perceptions of students' metacognitive strategies amongst the high- and average-achieving students. Data from the "Metacognitive Support Questionnaire" showed that there were significant gains in the students' perceptions of their metacognitive support implying that the majority of the students perceived that their learning environment was oriented towards the development of their metacognitive capabilities. The effect of the metacognitive interventions on students' achievement in the Light test resulted in students displaying the correct declarative knowledge, but quite often they lacked the procedural knowledge by failing to explain their answers correctly.