This paper examines the impact of school starting age on teenage marriage and motherhood in vietnam. The investigation uses data from the 2009 vietnam population and housing census and regression discontinuity methods to identify the causal effects of school starting age on teenage marriagea first in the literatureand early motherhood. Results show that girls who start school earlier are more likely to marry and/or give birth as teenagers than their counterparts who begin school later. School starting age impacts are heterogeneous across girl subgroups. The deleterious effects of starting school early are particularly pronounced for teenage girls who are members of ethnic minorities, whose mothers have relatively less education, and whose households are relatively poor. Girls that fall into these subgroups are more likely to benefit from a delay in school entry. Government may wish to adopt a more flexible approach to its age at entry regulations to allow disadvantaged girls the option of starting school later. 2019, Springer nature b.V.