This study aims to find out the effect of the English course designed with understanding by design on students' achievements, performances and opinions. The study was designed as a case study. The participants consisted of 13 sixth grade students in a private secondary school in Istanbul. Both qualitative and quantitative data collection tools were used. Quantitative data collection tool was performed in order to implement pretest and posttest. Since the number of the students in the classroom was not convenient to perform parametric tests, nonparametric test was implemented. There was no purpose of generalization in performing quantitative data since the tool used was nonparametric. The quantitative data were analyzed through Wilcoxon test. As for qualitative data; the performance products were evaluated according to the performance standards. Descriptive analysis was performed for the analysis of observation and content analysis was used for the analysis of the data obtained from the focus group interview. It was found that there was a significant difference in the achievement tests applied to the students at the beginning and at the end and the books and the traditional seating decrease students’ motivation. It was observed differentiated teaching techniques, games, videos and songs change the students' attitude towards the course. It was found that carrying out English in sports field was one of the most effective implementations to enhance students’ motivation. It was observed students' interest and motivation towards the course increased with the use of different materials and differentiation of the course environment; as a result, it was concluded that the success and motivation increased.