ILT (International Language Testing) is obligatory TOEFL preparation classes at EED UMY which help students to improve students’ TOEFL score more than 500. This study aimed to find out the effect of joining ILT class towards students TOEFL score at EED of UMY. The hypothesis was there is no effect of joining ILT class towards students TOEFL score at EED of UMY. The two research questions formulated in this study are (1) How are EED UMY students’ TOEFL score? (2) How is the effect of joining ILT class towards EED UMY students’ TOEFL score? This study is a quantitative research with cause-effect design. The sample of the study was 151 students of EED UMY batch 2013. The sample of the study was drawn by Total Population Sampling (TPS). The researcher took the secondary data from the ILT lecturer. In data analysis, the researcher used score categorization by Carson (1990) and Paired sample T-test through SPSS program version 17. The result of the study showed that: 1) there was increasing students’ TOEFL score after joining ILT class. The increasing was 63 point. 2) Ho was rejected ( = 0.000 < 0.005). It means there is an effect of joining ILT towards students TOEFL score at EED of UMY. Besides, the size of the effectiveness of joining ILT class towards students’ TOEFL score was large effect (0.99 > 0.50).