People generally develop some degree of competence in general informal reasoning and argument skills, but how do they go beyond this to attain higher expertise? Ericsson has proposed that high-level expertise in a variety of domains is cultivated through a specific type of practice, referred to as ‘deliberate practice’. Applying this framework yields the empirical hypothesis that high-level expertise in informal reasoning is the outcome of extensive deliberate practice. This paper reports results from two studies evaluating the hypothesis. University student (...) participants completed 12 weeks of deliberate practice in informal reasoning. Quantity of practice was recorded by computer, and additionally assessed via self report. The hypothesis was supported: students in both studies showed a large improvement, and practice as measured by computer, was related to amount of improvement in informal reasoning. These findings support adopting a deliberate practice approach when attempting to teach or learn expertise in informal reasoning. (shrink)