在同時具有實體資本和人力資本的疊代經濟體中，因為個人的實體資本和人力資本累積偏離了黃金法則路徑(Golden Rule path)，故市場經濟的成長軌跡無法達到最適。Del Rey and Lopez-Garcia (2013)發現，當教育技術在自身教育投入和父母人力資本外部性之間為一階齊次時，對教育課稅融通退休金的政策可幫助達成黃金法則路徑。然而實證證據顯示父母的人力資本外部性十分薄弱。本篇研究展示一旦父母人力資本外部性較弱，使得教育技術的階次小於一時，達成黃金法則路徑的最適政策為對教育補貼而非課稅。

In OLG economies with physical and human capital, the growth path of the decentralized market equilibrium fails to achieve optimality, because individuals’ accumulation of physical and human capital is in general different from that which maximizes welfare along the Golden Rule path. In an OLG model with the education technology being homogeneous of degree one in education input and a parental human capital externality, Del Rey and Lopez-Garcia (2013) found that education taxes with pensions can attain the Golden Rule social optimum. However, the empirical evidence suggests a weak parental human capital externality. Our paper shows that it is optimal to subsidize, rather than to tax, education, when the parental human capital externality is smaller when the education technology is homogeneous with less than one degree.