This work sought to obtain experimental evidence to corroborate cross-sectional patterns of development in
argument skills and to evaluate the effectiveness of an intervention designed to foster development of these
skills in academically at-risk 13- to 14-year-olds. Students participated in 16 sessions of a collaborative, goalbased
activity providing dense exercise of argumentive thinking. One condition included peer dialogues;
another did not. The former was the more effective, although both groups progressed. Participants showed
increased frequency of usage of powerful argumentive discourse strategies, such as counterargument, and
decreased frequency of less effective strategies. Quality of individual arguments (for or against a claim) also
improved, supporting the existence of a close relation between these two kinds of argument skills.