This study investigated the factors, such as students' foreign language enjoyment, their foreign language classroom anxiety, the teacher's language choice (English-only instruction versus English instruction with limited legitimate Japanese support), and demographics that affect improvement in English proficiency in EFL communicative classes. Ninety-three college students in Japan participated in this research, for which they completed a questionnaire after the seventh lesson of 14 total lessons during a semester. In addition to t-tests, a stepwise multiple linear regression analysis was performed using the dependent variable of the change in every student's scores between the midterm and the final examination and six independent variables: age, gender, nationality, the teacher's language choice, anxiety levels, and enjoyment levels. The results reveal that higher levels of enjoyment in class are significantly correlated with improvement in students' English proficiency. The present study suggests that enjoyment levels, instead of anxiety levels, affect improvement in students' English proficiency regardless of teachers' language choices. Therefore, it is important for teachers to provide classes that are enjoyable for students by motivating and providing the students with activities in which they will succeed, thereby ensuring their self-confidence.