The aim of this research was to discern the effects of computer assisted English instruction on English language preparatory students’ attitudes towards computers and English in a Turkish-medium high school with an intensive English program. A quasi-experimental time series research design, also called “before-after” or “repeated measures” design, was used in this research. As a sample, one group of students (20 female and 10 male) was randomly assigned. The research had two phases: traditional English instruction and computer assisted English instruction (CAEI). The instruments for data collection were a Scale for Attitudes Towards English and a Scale for Attitudes Towards Computers, which were given three times at intervals of two weeks. According to the findings, the students’ scores of attitude towards computers and English after CAEI increased significantly. However, the orrelations between the increases in the students’ attitude scores, their gender, and their monthly income were found to be insignificant. This research design is advised for researchers to see the variation and trend of measurements, in particular contexts in time.