Teachers are almost universally agreed that large classes "are exhausting, a cause of frustration, and a reason for failure in basic subjects". Their views about what constitutes a "large" class have changed considerably in recent years, however. The same author quotes figures for England to show that the optimum size of class that teachers thought most desirable was regularly about 3 to 5 pupils less than the current average! Parents tend to support the teachers' views about the desirability of small classes and frequently send their children to private schools for just this reason. Both teachers and parents argue that with smaller classes there is less strain on the teacher, and he can give more attention to individual pupils, and so improve achievement levels. Unfortunately, the research shows that the situation is not nearly as simple as this.