This study investigates: 1) The development of children's interpersonal negotiation strategies (INS) based on the theory of Selman, and 2) the possibility of predicting the level of (c) selecting specific strategy (INS) by the levels of the other 3 social information processing steps, which are (a) defining the problem,(b) generating alternative strategies, and (d) evaluating outcomes. Two hundred seventy-three elementary school children, 1st to 6th graders, are investigated by means of a structured dilemma-discussion interview and a questionnaire on two hypothetical dyadic interpersonal dilemmas. The results of the investigation indicate: 1) INS level is found higher in older children; 2) the possibility to predict the level of (c) by the levels of (a),(b) and (d).