This study modified the Ramanujam and Venkatraman (1987) questionnaire that was used to develop their model of planning system dimensions and planning effectiveness, and tested the model on a sample of private social service agencies. The criterion measures were level of planning sophistication, agency size, perceived environmental uncertainty, and relative competitive position. The sample was randomly drawn from private social service agencies which were members of the Community Council of Greater Dallas. Telephone interviews with fifty executive directors were conducted by a trained, impartial interviewer. Stepwise discriminant analysis was used to predict group membership between informal and formal planners. Of the nine dimensions in the model, three dimensions correctly classified 84 percent of the sample. The three dimensions were fulfillment of planning objectives, use of decision making techniques, and lack of resistance to planning. The level of perceived environmental uncertainty was another criterion set. Directors who perceived high uncertainty paid more attention to the external environment, used more decision making techniques, and relied on functional specialists when planning. Large and small agencies were classified by their annual budgets. Stepwise discriminant analysis using the planning system dimensions failed to reject the null hypothesis. Agencies reporting strong relative competitive positions placed greater …