He enrolled at the University of Buenos Aires Law School, where he was mentored by Professor José Manuel Estrada, graduating with a juris doctor in 1882.

The mercurial student began contributing articles and columns on a variety of subjects during law school, and continued in subsequent years.

This experience earned him a seat on Emilio Mitre's Railroad Regulatory Commission, which contributed to the orderly and rapid development of rail transport in Argentina, after 1889.

The text articulated his view as historian that Argentine politics would shift along roughly 18-year cycles and that reform could only evolve as quickly as the educational level of the public at large.

Matienzo retired from his professorship in 1927, when he accepted Socialist Party leader Juan B. Justo's invitation to join his ticket as a running mate.