The purpose of this study is to investigate the effects of a mathematics basis underachiever program on a mathematics achievement and mathematics attitudes. For this investigation, twenty eight-grade students as an experimental group were trained in a mathematics basis underachiever program by trained teachers in a middle school classroom for a period of 8 weeks. Twenty eight-grade students in another middle school, serving as a control group. Both groups were given a pretest and a posttest to check the mathematics achievement inspection tool(Likert-type Mathematics Attitude Survey; LTMAS) and a mathematics attitude inspection tool(KEDI, 2001). In the analysis of data Frequencies, percentiles, t-test were used. The results of the study are summarized as follows; First, the results showed that the experimental group demonstrated significantly higher differences than the control group in the mathematics achievement components of inequality equation, figure area and the whole in a mathematical achievement(p<.05). Second the results showed that the experimental group demonstrated significantly higher differences than the control group in the mathematics attitude components of positive mathematics attitude, negative mathematics attitude and the whole in a mathematical attitude(p<.05).