"Covariates included in this study were study center, child sex (female, male), birth order, mother’s ethnicity, parental highest education level and TV viewing time (hours/day), maternal age at delivery (in years), household monthly income at recruitment, and maternal sensitivity from a 15-min observation of mother–child interactions at 6 months. "

The big thing missing there are measures of parental behaviour and how much attention the kids get from adults. I would love to see an adjustment for parental screen time, or a study of the impact of parental screen time on academic performance.