" A program in Madagascar that simply told parents about the average income gains from spending one more year in school for children from backgrounds similar to theirs had a sizable positive effect on test scores, and, in the case of parents who found out that they had underestimated the benefits of education, the gains were twice as large.40 An earlier study in the Dominican Republic produced similar results with high school students.41 Since it is essentially free to have teachers simply pass on information to parents, this is so far the cheapest known way to improve test scores, among all the interventions that have been evaluated "

― Abhijit V. Banerjee , Poor Economics: A Radical Rethinking of the Way to Fight Global Poverty