This study examined the effectiveness of group investigation teaching technique in teaching "Light" unit 7th grade primary science education level. This study was carried out in two different classes in the Primary school during the 2011-2012 academic year in Erzurum, Turkey. One of the classes was the Experimental Group (group investigation teaching technique applied) and the other was the Control Group (traditional teaching methods applied). Students in the Experimental Group were divided into 6 groups and each group concluded 4 members since "Light" unit formed 4 subtopics. The subtopics names are a) absorption of light, b) refraction of light, c) lenses and d) prism of light. The main instrument for obtaining data was the Light Achievement Test (LAT), which was applied to groups both pre-test and post-test. The data obtained indicated that the students in the Experimental Group were more successful than students in the Control Group.