Teachers in Singapore and Hong Kong often come from the top third of their respective countries' college graduating populations. This is due to the fact that these nations place a high value on education and feel that only the most capable and knowledgeable individuals should be instructing their young people. In contrast, the majority of the teaching staff in the United States comes from the least educated third of college graduates.
This is due to the fact that the United States has a long tradition of placing a higher value on experience than education, and the widespread belief that anyone can be an effective educator provided they have the appropriate attitude and work ethic. In the United States, there are few exceptions to this norm, but in general, the majority of instructors come from the lowest third of college graduates.