The aim of our cross-sectional investigation was to explore prosocial behavior at the ages of 9, 11, and 13, and to reveal associations between this social behavior and some background variables such as age, gender, and parents' educational attainment. The participants were 185 Hungarian students and their teachers. Two Likert-type questionnaires (teacher and student versions) were developed and used in this study. These instruments proved to be highly reliable (Cronbach's a: 0.79-0.87). The results from both teachers and students indicate that sharing property and showing a positive attitude toward others are more typical of third-graders (age 9) than of older children. Conversely, standing up for individual interests during teamwork is most typical of the oldest group of children. Students and teachers also agree that third (age 9) and fifth graders (age 13) are more likely to help others than older children. The correlation coefficients for the different factors of prosocial behavior become progressively weaker with age. Cooperation and helping appear to become independent of each other. Our regression analyses reveal that parents' educational level explains equally low shares of the variance in the measured areas of the prosocial behavior for all three age groups.