Introduction: In the process of continuing education, nurses are one of the most important audiences in hospitals, which need development of teaching and learning methods to enhance their performance. This research was based on the need for proper training of Intensive Care Units (ICU) nurses for arterial blood gas interpretation skills in the care of critical patients and evaluated the effect of formative assessment with appropriate feedback for development of this skill.

Methods: This was a quasi-experimental study with 90 nurses working at critical care settings of three hospitals. The samples were selected based on the available sampling method and inclusion criteria. Arterial blood gas interpretation skills of nurses were measured before and after the educational intervention. Results were compared using descriptive and inferential statistical methods using the SPSS Inc software (Released 2007. SPSS for Windows, Version 16.0. Chicago, SPSS Inc).

Results: The primary mean score was 13.86 ± 3.7 for the oral group, 12.93 ± 2.27 for the written group and 12.43 ± 2.51 for the control group. Also there were no significant differences between the three groups before the intervention (P = 0.157). The mean score after intervention was 20.33 ± 1.58 for the oral group, 18.40 ± 1.84 for the written group and 15.96 ± 1.56 for the control group. The mean scores between groups were significantly different after the intervention (P < 0.001).

Conclusions: This study showed that using formative assessment and providing proper feedback is effective on learning and using formative assessment, with written and oral feedback improving arterial blood gas interpretation skills. Therefore, it is recommended that formative assessment with written and oral feedback be used in educational programs.