Introduction: Written action plans (WAPs) are instructions that enable asthmatics to manage their condition appropriately and are recommended by current asthma clinical practice guidelines (CPGs). However, general practitioners (GPs) rarely draft WAPs for their patients. An interactive, case-based workshop for asthma, combined with an objective structured clinical examination (OSCE), was developed to increase GPs' knowledge and use of WAPs in Quebec. Methods: The study compared 24 GPs receiving an OSCE preworkshop and 12 months post-workshop (group 1) with 16 GPs receiving an OSCE preworkshop and at 6 and 12 months post-workshop (group 2). Participants received no feedback on their OSCE performance. During the workshop, which presented a preformatted tool to aid drafting of the WAPs, all 40 GPs worked individually and in small groups to answer questions on a hypothetical clinical case and then discussed the responses with a facilitator and an asthma specialist. Results: Only group 2 GPs showed a significant improvement in knowledge of WAPs 12 months post-workshop (p =0.01). The likelihood of prescribing WAPs to patients increased in group 2 to a degree approaching statistical significance (p =0.070), and there was a borderline nonsignificant trend for prescribing practice to improve more among group 2 GPs than among group 1 GPs (p =0.052). There was also a nonsignificant trend for 6-month OSCE to increase attendance at the 12-month OSCE. Discussion: An interactive workshop employing a preformatted WAP tool and a reinforcing OSCE at 6 months yielded improved knowledge of WAPs at 1 year. Although originally developed as a form of evaluation, the OSCE appears to have formative value even when correction is not provided and may increase the effectiveness of continuing medical education interventions to enhance CPG implementation.