Recent studies show that texting-based interventions can produce educational benefits in children across a range of ages. We study the effects of a text-based program for kindergarten parents, distinguishing a general program from one that adds differentiation and personalization based on the child's developmental level. Children in the differentiated and personalized program were 50 percent more likely to read at a higher level (p<0.01) compared to the general group; and their parents reported engaging more in literacy activities by 0.31 standard deviations (p<0.01) compared to the control group. Effects were driven by children further from average levels of baseline development.