They do share a common cause: a lack of money. Increasing guaranteed income improves those measured outcomes: http://www.mitpressjournals.org/doi/abs/10.1162/003465399558... That is, by giving their parents money you improve children's cognitive performance. I'm not sure what more causal evidence you are looking for. Also see https://files.nyu.edu/mw109/public/loken_mogstad_wiswall_fam... for the statistics involves.