In 1972 it was announced that the English speaking campus at the Inter-American University in San Germán would close the following year. An international group of concerned parents started planning a new school. They wanted to create an institution with high academic standards. They also wanted to take advantage of the bilingual, cultural richness and diversity of Puerto Rico.

It was to be a school where students could interact and learn from each other in an atmosphere of freedom, tolerance and mutual respect. Southwestern Educational Society (Sociedad Educacional del Suroeste) was founded in 1973 as an independent, nonprofit organization to achieve these goals. The initials SESO have become the common name used by the community to identify our school.