This paper reports on a study to examine mental computation strategies used by Year 1, Year 2, and Year 3 students to solve addition and subtraction problems. The participants in this study were twenty five 7 to 9 year-old students identified as excellent, good and satisfactory in their mathematics performance from a school in Penang, Malaysia. The students were interviewed individually and asked to solve 6 questions consisting of 1, 2 and 3 digits addition and subtraction problems mentally without the use of pen and paper. The students were also required to explain how they arrived at their answer. Findings from this study showed a range of strategies employed by the students even though addition and subtraction mental strategies are not formally taught to Year 1, Year 2 and Year 3 students. The different types of addition and subtraction strategies used were highlighted. The strategies for 1-digit, 2-digit and 3-digit mental computation of both addition and subtraction problems were compared. Further, the students employed intuitive mental computation strategies and there are qualitative differences in these strategies which may prove invaluable to help teachers in strengthening students' understanding of the number concepts. Pedagogical and curricular implications arising from the findings were discussed. (Contains 7 tables.)