In the present study the Impact of the dispersive effect of STEM Education on the hierarchical Structure of the Cognitive Domain of Bloom's Taxonomy and its role on enhancing the students' achievement and attitude towards learning sciences were investigated. In QSTSS, STEM lessons followed the "Do-Then-Explain" Model in which the students start the activities by creating products, evaluating and analyzing them rather than with remembering and understanding. This way of delivering the content inverses Bloom's taxonomy as it starts from the high skill levels of the cognitive domain descending to the lower ones. Pretest and posttest were used to track the improvement in the achievement of the students due to applying the STEM program. A questionnaire was distributed to measure the students' attitudes towards sciences due to STEM education. By the end of the program, the students were interviewed to check their dispositions towards future careers. The results show that STEM education whether it is implemented as a separate course or as projects integrated within the curriculum has strong positive effects on the students' attitudes towards learning and joining engineering or medical faculties in the future. It was also shown that STEM education improves the achievement of the students in the standardized tests. The scope of application of the study results will consider valid for all students in the secondary schools in Doha/Qatar. Therefore, we strongly recommend generalizing and applying STEM programs in all school levels.