The primary school pupil-to-teacher ratio is the number of pupils enrolled in primary school divided by the number of primary school teachers (regardless of their teaching assignment).
Teachers of a large class can dedicate less time to each pupil than in a small class. For the pupils, crowded classrooms make it difficult to concentrate on the material and to learn. The results of overcrowding are lower academic achievement and increased dropout rates.
Liechtenstein, Denmark, and Sweden have the lowest pupil-to-teacher ratios in primary school (were than 10 pupils per teacher). Most of the developed countries (including the countries of Central Europe or the CIS) have 10-20 pupils per teacher, while the world's average is around 25.