Altamirano Álvarez, Martha Leonor. “Manipulative Materials to Develop Classification and Seriation Concepts in Early Childhood Education”. Revista de Investigación Educativa Niveles 3, no. 2 (November 9, 2026): 332–341. Accessed November 9, 2026. https://niveles.esprint.tech/index.php/niveles/article/view/128.