The main goal of this study was to trace the evaluation function in technological problem solving process. This study fouced on : (1) identifying the process path of evaluation cycle, (2) identifying the conceptual constituents of evaluation (3) the formulation of designing space/making space/evaluation space model characterizing these cycles. 5 grade 6 students and 6 grade 4 students participated in the study. This study required the case study methods in data collection and analysis. The data collection methods were used the video recording, the interview, and the field notes of researcher. The students' performance procedures and thinking aloud were video recorded. The collected data were transcribed verbatim. Each students' performance was coded with respect to not only the participant's explicity stated intent but also the intent suggested one or more of their trials. Each student was provided with a copy of a design brief that described the technological problem to be solved. The problem was to construct the tallest possible tower. The results of this study were as follows: The results are presented in the order of the research questions given above.1) The evaluation recurred cyclically and become intertwined, until the student eventually decided that the task has been completed. Particularly, the movement between making space and evaluation space revealed the cyclical aspect. 2) The conceptual constituents of the evaluation space revealed an interesting variety of positions adopted by the students. 3) The model of the process performed by students was developed. The model offered a graphic representation of action-space. The evaluation space was included in the designing space and making space.