Munser-Kiefer, M., S. Martschinke, A. Lindl, and A. Hartinger. “Development of Self-Concept in Multi-Grade 3rd and 4th Classes”. International Electronic Journal of Elementary Education, vol. 15, no. 4, June 2023, pp. 343-56, https://www.iejee.com/index.php/IEJEE/article/view/2010.