Ina large-scale school improvement project in Indonesia the implementation, effects and costs of initiatives to increase parental involvement were compared with those of other interventions (teacher development, educational management and books and learning materials). It turned out that although parental involvement was not implemented very successfully in schools, this intervention is quite effective in improving student achievement. In comparison with the other interventions it is in fact the most efficient because costs are relatively low. Recommendations a-re given to implement parental involvement further, and to raise its effects without raising the costs