Number of children vs education level

Well, i was reading my readings in preparation for my Nation Building Tutorial on monday. I came across this interesting statement from one of the readings;

"The number of children in Malay families has also been commonly cited as an important casual factor contributing to the poor performance of Malay students............. in 1985, Goh Chok Tong armed with an impressive array of statistical data showing the correlation between large families, poverty and acadamic performance, urged Malays to have smaller families in order to improve their educational standings....... However this is contridicted by the 1990 census which indicated that the mean number of children among parents with university education was 1.36 compared to 1.58 for those with secondary education, 2.37 for primary school educated and 4.6 for those without education...."

cited from (The Singapore Dilemma: The Malay Educational Marginality by Lily Zubaidah Rahim)

Something to think about??
Why do higher educated people have less children?