An ideal group size is hard to obtain in small group settings; hence there are groups with more members than others. The purpose of the study was to find out whether group size has any effects on students' mathematics achievement in small group settings. Two third year classes of the 2011/2012 academic year were selected from two schools in the Central Region of Ghana for the study. The two classes constituted the control and experimental groups respectively and consisted of 50 students in the control group and 47 in the experimental group. The experimental group was subdivided into 12 groups made up of groups of 3 members, groups of 4 members and groups of 5 members using stratified and simple random sampling. The students' pre- and post-test scores served as the data for the study. The results of the study showed no significant difference in the mean scores of the three subgroups of the experimental group.