Recent studies show that texting-based interventions can produce educational benefits in children across a range of ages. We study effects of a text-based program for parents of kindergarten children, distinguishing a general program from one adding differentiation and personalization based on each child's developmental level. Children in the differentiated and personalized program were 63 percent more likely to read at a higher level (p < 0.001) compared to the general group, and their parents reported engaging more in literacy activities. Effects were driven by children further from average levels of baseline development, indicating that the effects likely stemmed from text content.