Many educators recommend the "Geometric Supposer" as exemplary software. This study compared the achievement of one high school class that used the software and a similar class that did not. The treatment class used the software once every 2 weeks throughout the school year. The SRA Achievement Test was used as a pretest and the Houghton-Mifflin Modern Geometry Test was used as a posttest. Four separate (Analyses of Covariance) ANCOVAs were calculated to determine the effect of the treatment on total geometry achievement, lower level items, application items, and higher level items of the posttest. The treatment class scored significantly higher on all except the lower level items. Traditional teaching methods seemed to address lower level knowledge and comprehension. (YP)