The present study investigated the relationship between age and one type of environmental factor, namely, type of school (i.e., private vs. public), and the development of mental planning ability, as measured by the Tower of London (TOL) test., Methods: Participants comprised 197 public and 174 private school students, ranging in age from 4 years and 9 months to 8 years and 6 months. Besides the TOL test, students were administered Raven's Colored Matrices., Results: Results confirmed the findings of previous studies that both age and school type are important predictors of mental planning. Furthermore, results also suggest that the relationship between type of school and mental planning ability cannot be accounted for by differences in students' fluid intelligence., Conclusion: In the present study, the TOL test continued to differentiate public from private school students, even after we controlled for the effect of differences on the Raven test.