Students' abstract reasoning abilities can differ from one society to another. Students' profiles play significant roles in these differences. The aim of the study is to determine the relationship between middle school students' cognitive development levels and their profiles (age, gender, and science achievement) using the Science Cognitive Development Test (SCDT) in Turkey. The subjects (N=445) were drawn form 7th and 8th grade students at private and public middle schools in five cities. While significant relationships were not found between students' cognitive developments and their genders and ages, a relationship was found with science achievement. The Science Cognitive Development Test (SCDT) is appended. (Contains 8 tables.)