Co-published by UNESCO Bangkok and Results for Development (R4D), this report looks at the benefits of primary education and estimates the economic cost associated with large populations of OOSC in seven Southeast Asian countries – Cambodia, Indonesia, Lao PDR, the Philippines, Thailand, Timor-Leste and Viet Nam. To help education policy makers and decision makers gain a clear understanding of the significant economic incentives linked to educating OOSC, the report uses two methods to estimate the economic loss resulting from not educating these children. The first estimation approach uses labour market data to estimate the total earnings which will be forfeited in the near future due to undereducated workers if primary school enrollment patterns do not change. The second approach is based on cross-country regressions that estimate the relationship between national education attainment and per capita income.