Decision making, a complex mental activity underlying the act of choosing from among the alternatives in attaining a goal constitutes the core component of planning, a higher order cognitive process as per the PASS theory of intelligence. An attempt, therefore, has been made in the present study to examine the development of planning behaviour in children with increasing age and grade. Marker tests of planning were administered to a group of 60 children, 20 each from Grades Three, Five and seven in order to see the group difference among them in respect of planning at its various levels. Results revealed age and grade related changes in the development of planning behavior at lower levels, but not at higher level. The findings have been discussed in terms of developmental changes in children in cognitive functioning with regard to planning and consequences of formal schooling and suggestions have been made for the improvement of the planning skill through remedial training.