The largest and most up-to-date study performed so far shows that the school progress of children with parents of the same sex does not differ from their peers in the United States today.
This study, published in the leading journal Demography, also provides large-scale evidence that children adopted by same-sex parents do as well as children adopted by different-sex parents.
The paper shows that, historically, this was not always the case. In areas with high levels of stigma toward same-sex couples children of same-sex parents used to be more likely to lag behind in school, especially those adopted by same-sex parents. As attitudes toward same-sex couples became more positive over time, these differences disappeared. Today, no differences are found between children of same-sex parents and children of different-sex parents among all groups and areas studied. Besides general reductions in social stigma, another likely reason why these differences existed in the past but not anymore today is changes in access to adoption. Same-sex couples were more likely to adopt children with special needs (who are more likely to fall behind in school); this tendency might have become less strong as adoption became more accessible to same-sex couples.