BACKGROUND: Training is a common and cost-effective way of trying to improve quality of care in low- and middle-income countries but studies of contextual factors for the successful translation of increased knowledge into clinical change are lacking, especially in primary care. The purpose of this study was to assess the impact of contextual factors on the effect of training rural healthcare workers in Kyrgyzstan and Vietnam on their knowledge and clinical performance in managing pediatric patients with respiratory symptoms. METHODS: Primary care health workers in Kyrgyzstan and Vietnam underwent a one-day training session on asthma in children under five. The effect of training was measured on knowledge and clinical performance using a validated questionnaire, and by direct clinical observations. RESULTS: Eighty-one healthcare workers participated in the training. Their knowledge increased by 1.1 Cohen's d (CI: 0.7 to 1.4) in Kyrgyzstan where baseline performance was lower and 1.5 Cohen's d (CI: 0.5 to 2.5) in Vietnam. Consultations were performed by different types of health care workers in Kyrgyzstan and there was a 79.1% (CI 73.9 to 84.3%) increase in consultations where at least one core symptom of respiratory illness was asked. Only medical doctors participated in Vietnam, where the increase was 25.0% (CI 15.1 to 34.9%). Clinical examination improved significantly after training in Kyrgyzstan. In Vietnam, the number of actions performed generally declined. The most pronounced difference in contextual factors was consultation time, which was median 15 min in Kyrgyzstan and 2 min in Vietnam. DISCUSSION AND CONCLUSION: The effects on knowledge of training primary care health workers in lower middle-income countries in diagnosis and management of asthma in children under five only translated into changes in clinical performance where consultation time allowed for changes to clinical practice, emphasizing the importance of considering contextual factors in order to succeed in behavioral change after training.