Purpose: The quality of resuscitation and effective leadership are decisive for the outcome of a resuscitation. Nurses are usually the first responders upon cardiac arrest. Therefore, we started the “proficiency check” project, which aims to improve nurses' resuscitation and teamwork skills. This article describes the effectiveness of the proficiency check and nurses' experiences with it. Design and methods: This study was done among intensive care nurses working on a pediatric ICU (PICU) in the Netherlands. It was designed as a mixed-methods study combining a quantitative and a qualitative approach. Quantitative data were obtained through a pre-posttest comparison of nurses' resuscitation and teamwork skills, in a simulation setting. Qualitative data on nurses' experiences were collected through semi-structured individual interviews. Results: Both resuscitation and teamwork skills improved significantly. In 39 nurses (32%), the improvement of both resuscitation and teamwork skills after the intervention was large (effect size >0.8). The experiences of nurses regarding the proficiency check were diverse: on the positive side, increased knowledge and confidence were reported, whereas negative experiences related, among other things, to stress and anxiety. Conclusions: Resuscitation and teamwork skills of PICU nurses can be enhanced by the ‘proficiency check’ studied here. This simulation-based training can be further improved by incorporating the nurses' experiences. Practice implications: A simulation-based assessment for resuscitation may play an important role in a PICU, and possibly for other skills and in other settings as well. Particular attention should be paid to the stress that many nurses experience due to skills assessment.