This study was conducted on year 4 students enrolled in the Bachelor of Education program for Cycle one teacher candidates. The effect of practicing mental calculation strategies in improving students’ numeracy proficiency was put under some tests to measure its effect in a scientific way. A Pre-quiz was conducted before with no prior practice done in order to check the strategies the students were using in performing calculations. After four weeks practice and implementation which focused mainly on addition and subtraction questions, as a result a post quiz was written by the students. The improvement results were recorded and analyzed. After four weeks of practicing multiplication and division questions, another post quiz was written by the students as a result of that. Once again, the improvement results also were recorded and analyzed. Furthermore, interviews and observations also were used to record changes in the students’ perspectives about using the mental strategies and their feelings toward their numeracy level. The results of the study showed that practicing the mental strategies had a significant impact on the students’ numeracy proficiency and their perspective toward their mental strategies. The study also showed that more practice had a significant impact on the students’ confidence as well as their ability to perform different mental strategies in their daily life. Keywords: Calculation strategies, Numeracy proficiency