I examine the importance of human capital for economic development in Thailand during the period of high economic growth and structural transformation (1985-2000), using labour force survey data. The three main chapters attempt to estimate the effects of education, as a measure of human capital, on three major outcomes in the Thai labour market, namely (i) earnings; (ii) sector of employment; and (iii) earnings inequality. I address the endogeneity problem of education using an education policy shift—the change in the compulsory schooling law—that produces exogenous variation in education. The three main chapters adopt distinct modelling frameworks. The details of each of the main chapters are as follows. The third chapter investigates how education increases earnings and the probability of being in the non-agricultural sector. As the education policy shift influences educational attainment in a discontinuous way, a regression discontinuity (RD) framework is adopted to identify the average returns to education and the effect of education on the sector of employment. It is important to emphasise that the RD technique constrains the effects of education on the two outcomes to be linear and to be applicable only to sub-populations. My results confirm significant effects of education on both earnings and the sectoral sorting process. In addition, there are heterogeneous effects of education by gender. The fourth chapter is an extension of the previous chapter. I allow the returns to education to be heterogeneous across education levels and sectors of employment, while attempting to estimate the returns for the entire population. I use a control function (CF) approach and a double selection correction to estimate the sectoral earnings process, while jointly accounting for the choice of education and the selection into sectors and paid employment. I find that the returns to education are non-linear and higher in the non-agricultural sector especially for medium and highly educated workers. This suggests that human capital plays a crucial role in facilitating a structural transformation towards the non-agricultural sector. In the final chapter, I study how the increased primary education completion rate affects earnings inequality. While there exists a burgeoning literature on the average returns to education, less attention has been devoted to estimating the effects of education on the distribution of earnings. I identify the effects of primary education completion on earnings at different points of the distribution, and thus earnings inequality, using a recently developed approach, called regression discontinuity distributional treatment effects. My results suggest that the increased primary education completion rate reduces earnings inequality as the returns to primary education are larger for the poor than the rich.