Caso completed a law degree in 1919 and immediately started teaching at the National Autonomous University of Mexico. The systematic legal training he received would mark his archaeological and administrative work throughout his life. While a young lawyer, Caso visited the then-remote hilltop ceremonial center of Xochicalco in Mexico's state of Morelos. The art and architecture of Xochicalco fascinated him and turned his mind to the archaeological study of pre-Hispanic Mexico. While he continued to work in legal projects associated with commercial institutions, he began a program of study at Mexico's Museo Nacional. There, he took classes in pre-Hispanic history, ethnology, and archaeology with influential teachers as Eduard Seler, Hermann Beyer, and Manuel Gamio, with whom he often debated, posing alternative interpretations. At the age of twenty-nine, he obtained a master's degree in philosophy (with a specialty in archaeology) from the Escuela de Altos Estudios. After that, he dedicated himself to the study of pre-Hispanic cultures and contemporary Indigenous peoples. His rigorous methods of interpretation were evident in his first essay on "patolli" and other pre-Hispanic games, and it was clear to his colleagues and teachers that a powerful new professional voice had arrived.