This study aims to develop a computer program for the identification key to insect orders (Arthropoda: Hexapoda) and to investigate its effectiveness as teaching material. Secondly, this study is aiming at whether this program improves students' computational thinking skills or not longitudinal quasi-experimental design. Firstly, the study is based on a longitudinal design involving repeated observations of the same variables over long periods and it is a repeated cross-sectional study also. Secondly, this study is based on a quasi-experimental design. According to this, there are two main groups selected for the study as the ones who took the course and the ones who didn't. There are two subgroups in those groups also the ones who identify the insects by dual diagnostic key and the ones who use the computer program developed by the researcher based on the dual diagnostic key. The population of the study consists of 621 students who took the courses related to entomology and 470 students who didn't take the course in the education period of 2010-2020 summing up 1091 students in total. The first indication of this study is that the computer program developed for the identification of insects is very effective for the students who took the course comparing the one using a classical method for the identification of insects. The second indication of this study is that the computer program developed for the identification of insects is very effective to improve the computational thinking skills of the students in terms of abstraction, automation, data analysis, decomposition, pattern generalization, pattern recognition skills. Finally, it can be concluded that computer program used for the identification of insects is very effective irrespective of whether the instruction is taken or not.