The aim of this study is to determine the effects of Group Investigation technique and Traditional Teaching methods on academic achievement of sixth grade students at unit of the “earth’s crust consist of what”. The sample of this study consists of 62 6th grade students who were taught in an elementary school during the 2010-2011 academic years. As the data collection instrument, Academic Achievement Test (AAT) was used. This study carried out in two different groups. One of the groups was selected randomly as the Group Investigation Group (LIG) and the second was selected as the Traditional Teaching Group (TTG). The data obtained on instruments were evaluated by using descriptive statistic, independent samples t test, paired sample t test and effect sizes. As the result of the research revealed that Group Investigation Group (LIG) is more successful than Traditional Teaching Group (TTG).