This study investigates the perceptions of Saudi Arabian primary school teachers in Years 4, 5 and 6 and discusses the effects of class size on teaching. The data comes from 30 teachers who teach small classes in two private schools, and 37 who teach large classes in two state schools in Alhafouf, Saudi Arabia. The study discusses whether different numbers of students in class could have an impact on teachers' perceptions and teaching practices. The data show that teachers in both small and large classes believe that class size has some impact on their teaching. Teachers in large classes report that they usually use a limited range of teaching methods, which tend to be more teacher-centred. The data show that all teachers in both small and large classes believe that class size has some impact on their teaching. In addition, the majority of participants say that they prefer to teach a class which contains 15 to 20 students. It has been highlighted in this study that there are many barriers and difficulties, especially with regard to lesson time, which most teachers in large classes could face regarding the management of students' behaviour and the assessment of students' performance. Empirical evidence suggests that class size is still the major aspect affecting teaching.