In 1970, the average class contained 22.3 students. Today, the average is 17 students per teacher. Yet the National Assessment of Educational Progress, the gold-standard test of academic achievement given every two years to students in grades four, eight and 12 nationwide, shows no discernible educational benefit in reading scores for children in smaller classes. Many other factors do seem to influence students' reading scores. The presence of at least one parent at home who attended college bodes well for reading performance.
Race correlates strongly with reading achievement.
But class size has little to no impact. Now there are some researchers who have suggested that radically reducing class sizes, say from 25 to 15, would positively affect student performance. And reducing the average class from 25 to 20 would net each student only a few extra seconds of individual attention anyway. Actually, in light of the anti-instruction bias prevalent in the teaching world right now, it's curious that so much attention is given to class size. Teachers, after all, are discouraged from lecturing or instructing their students directly.