Teacher shortages are among the most critical gaps that undermine educational performance, especially in developing countries, where there tends to be inequality in human resource allocation. This article therefore aims to study the impacts of teacher shortages on educational outcomes in a developing country by using Thailand as a case study. Using school-level survey data from the Program for International Student Assessment (PISA) in Thailand, estimates from the stochastic frontier analysis models indicate that teacher shortages are a serious problem that has a negative effect on the educational performance of Thai students, especially those living in rural areas. Furthermore, teacher shortages in certain subject fields are shown to have a spillover effect on other subject fields as well since teachers end up having to teach subjects that are not their specialization and to teach students of various ages and class levels mixed together. Therefore, effective teacher resource allocation should be tailor-made by taking into account the differences among schools such as school size or location since such factors play an important role in students' educational outcomes in developing countries.