Data are presented that focus on the nature and development of argumentative reasoning. In particular our study describes how support for or against an issue affects memory for critical parts of an argumentative interaction, judgments of argument goodness, and the content of the reasons given in support of one view versus another. Two other factors were examined: developmental differences in argumentation skill and the conditional nature of supporting one side of an argument across varying contexts. Our results show that even (...) seven year old children can recognize, identify, and use the basic components of an argument to provide evidence for and make judgements about their favored position. Moreover, if position support is held constant across all age groups of students, seven year old children were found to give reasons and explanations that were highly similar in content and principle to college students. The same similarities held across age with respect to biases in memory and judgements of argument goodness. The primary difference between children's and college students' argument behavior lay in the side of an argument the students chose to support. Seven year old children and some eleven yearold children supported positions that impute more value to friendship and social consequences than to the maintenance and advancement of individual rights, as specified in a contract agreement. The similarities and differences across development are discussed with respect to a theory of argumentation that speaks to the importance of understanding the nature of goal conflict and a theory of intentionality in predicting how arguments will be represented and resolved. (shrink)