Preschoolers scored about the same on the PPVT whether or not their mothers worked more or less than 26 weeks in the previous year. In fact, children with mothers strongly attached to the labour market scored slightly above the national average and those with mothers less attached to the labour market scored slightly below. The authors explain this unexpected result by noting that mothers strongly committed to the labour market read as frequently to their children as mothers who are less active in the labour market. Children whose parents read little or almost never to them, all other factors being equal, score 5.8 percent lower than children whose parents read to them several times per day, and 3.9 percent lower than children read to once per day. A further implication of this result is that mothers, who are time constrained due to work and family responsibilities, are spending less time on activities other than interacting with their children.
Maternal education is also important to preschool vocabulary skills.
The authors found a strong positive correlation between a mother's level of education and her preschooler's vocabulary skills. In fact, the mother's education is a more important factor than earned family income. One theory is that mothers with higher education talk more frequently to their children in the very early years, resulting in a significant head start in vocabulary. Another theory is that higher education is an indication of higher innate capacities of the mother, which she passes on genetically to her child. The authors do not deal with this question in their paper.