Brain cells are basically storage devices and the 'real' brain or intelligence is set by one's ability to associate the right cells for the right purpose at the right time. Human intelligence is roughly proportional to the number of brain-cell links. However, projections and creative associations do require more sophisticated 'data mining' capabilities. An infant's intelligence develops at a rate set mainly by the environment surrounding it - external stimuli, nutrition, sense of security, etc. By the age of 4 or 5, a child's IQ capacity is more or less set and it becomes evident even at this early stage that all children are not equal intelligence-wise.
Some kids are 'smarter' than others.
Statistically speaking, roughly one third of the kids of a given age group are 'A' pupils, one third 'B' and one third 'C'. Of course, not everyone can be an Einstein. A society cannot handle too many chiefs or not enough Indians. One must strike a proper balance of 'free' thinkers and 'slaves'. The government controls the educational system in Korea, and it is unrealistic to overhaul the system, which has persisted for several centuries, in a few years.