There's a distinction between A parent and all parents. Disproportionately more parents in low income areas (where kids have worse prospects already) will have

There's a distinction between A parent and all parents. Disproportionately more parents in low income areas (where kids have worse prospects already) will have very poor education themselves (possibly struggling with basic reading skills) and also possibly additional problems with drug/alcohol abuse etc. Not the sort of people who will be skilled at choosing curriculum and enforcing study.