The purpose of this study is to determine the levels of high school mathematics teachers in achieving mathematics instruction via computer algebra systems and the reflections of these practices in the classroom. Three high school mathematics teachers employed at different types of school participated in the study. In the beginning of this qualitative analysis, the researchers provided the teachers with in-service training titled Computer-Assisted Mathematics Instruction Workshop regarding the integration of the Mathematica software which is a computer algebra system in learning-teaching environments. The participating teachers then conducted computer-assisted mathematics instruction activities in their classroom via the Mathematica software regarding the graphs of quadratic equations (parabola). Semi-structured interview and observation forms were used as data collection tools in the study. The data were analyzed using the descriptive analysis method. As a result of evaluation, it was found that before the Computer-Assisted Mathematics Instruction Workshop, the participants either never implemented technology integration or implemented it on the elementary level which is replacement. After the workshop, it was observed that the teachers achieved the technology integration in classroom implementations on the level of transformation and the top level of amplification and showed improvements in this matter. In the observations made after the workshop, it was seen that the teachers generally employed a student-oriented education approach and encouraged students to facilitate their own learning and make their own inferences utilizing computers and worksheets. It was observed that this situation led to changes in classroom routines and contributed to students' acquisition of deeper comprehension by their own efforts. Additionally, it was understood that the students or the teachers did not have any difficulty in using the computer-assisted mathematics instruction materials prepared in Mathematica.