The purpose of the current research was to represent the process of aptitude assessment in the academic guidance of students. It was a qualitative study with grounded theory design. For this purpose, 12 experts in the field of aptitude assessment and academic guidance with doctorate degrees in educational sciences and psychology were studied with the purposeful sampling method and using in-depth interview. After collecting, recording and coding, the data were categorized into main categories and they were analyzed using Corbin and Strauss coding techniques, open coding, axial coding and selective coding. Based on the obtained results, aptitude assessment was chosen as the core category. The causal conditions were: identification of assessment dimensions/factors (individual-social and psychological) and skills and experiences. The context and situation of assessment were chosen as the background conditions and the continuous assessment of aptitude was chosen as the mediating condition. The strategies used, were identification tools, including: observation, interview, experts' opinion, teachers' opinion, self-expression, parents' opinion, tests, physical measurements, situational assessment, peer assessment and individual work portfolios. Finally, successful performance and feeling of satisfaction were introduced as the result of this model. Due to the fact that aptitude assessment is one of the important and vital factors of academic guidance, and merely emphasizing the tests does not provide accurate knowledge of people, it is suggested that the policy makers of the educational system put the use of process assessment, situational assessment and various tools in their agenda in order to strengthen and improve the academic guidance process.