The aim of the study was to investigate the effect of Microsoft Math Tool (graphical calculator) on students' achievement in the linear function. The study employed Quasi-experimental research design (Pre-test Post-test two group designs). A total of ninety-eight (98) students were selected for the study from two different Senior High Schools (SHS) in Accra, Ghana. The two schools were categorized as control group of forty-eight (48) students and experimental group of fifty (50) students. The analysis of data was done using independent t-test with alpha value (a) = 0.05. Pre-test assessment conducted at the beginning of the study shown no significant difference, t (95.720) = -0.441, p = 0.660 between the control and experimental groups. This indicated that the two groups were homogeneous. The experimental group received teaching instruction using the graphical calculator while traditional lecture method was used to teach the control group by the same instructor. Results revealed that there was significant differences, t (96.000) = -6.984, p = 0.00 in students' performance between control and experimental. This suggested that mathematics teachers and curriculum or textbook developers should introduce the use of the graphical calculator to improve students' performance in mathematics education, particularly linear and quadratic functions.