March 6, 1973 – First public meeting at the Firehouse in Mayaguez. Seven parents were elected to form the Board of Directors of the newly founded Southwestern Educational Society (SESO)
August 1973 – SESO opened on the 2nd floor of the YMCA in Mayaguez. Eighty-eight students from Kinder through 8th grade were grouped into five classrooms. Mrs. Nilda Rosario was Head Teacher – Principal. The school had a budget of $72,000 (tuition – $54,000 and donations of $18,000).
Summer 1975 – Through the arduous work and dedication of a group of parents of the first generation of SESO students, SESO transitioned from a rented building in Obispado to a larger building located in the Cuba Sector in Miradero. This building would serve as the foundation and remain to be a part of the SESO facilities today. These parents’ children started SESO in 1973 and would become part of the first groups of SESO graduates. There were 150 students from K-9th grade and Mr. Ralph González became the 1st School Principal.
April 1991 – SESO received Middle States Accreditation (MSA).
November 1992 – Lighting for the covered court became a reality thanks to a donation from Digital Equipment Corporation and the assistance of the school Parent – Teacher Organization (PTO).
November 1993 – SESO celebrated its 20th Anniversary at the Mayaguez Hilton. The newly constructed Snack Bar and Student Lounge were inaugurated.
August 1994 – Project “SESO 2005”, a vision for the facilities development as part of the strategic planning process by the Board of Directors under the leadership of school director Miguel Arzola-Barris, Esq., was unveiled.
August 1995 – The computer lab was equipped with twenty-five stations.
April 1996 – Inauguration of restroom facilities at the Covered Court. Pre-Kinder services were extended to a full day program.
September 1996 – Inauguration of the new administrative offices and facilities.
May 1998 – Plans for the multipurpose building and classrooms’ wing were presented to the school community.
June 1998 – Gala celebration at “Casa del Medico” and a Family Day at the “Club Deportivo del Oeste” in celebration of the school’s 25th Anniversary.
January 2000 – Groundbreaking for the multipurpose building.
August 2000 – Inauguration of the multipurpose building and Day Care Program.
March 2001 – Student enrollment reached 800.
May 2001 – Annual grade promotions and graduation ceremonies were held for the first time on school facilities.
August 2001 – An Accreditation for Growth visiting committee positively recommended SESO for MSA re-accreditation.
August 2002 – Completion of Project “SESO 2005”. The facilities included High School and Elementary School libraries, a Cafetorium that could accommodate up to 800 students, a new Computer Lab, a state-of-the-art Science Lab and an access ramp in compliance with ADA regulations and an inclusive policy.
February 2003 – Venice Masquerade Fund Raising Gala and Fashion Show were held in celebration of the school’s 30th Anniversary.
August 2004 – Inauguration of Pre-School Building and the access beltway around campus. SESO becomes an independent Regional Science Fair site.
February 2007 – First ever SESO Family Fair held on school grounds.
August 2013 – SESO celebrated its 40th Anniversary.
October 2016 – SESO received re-accreditation from Middle States Association (MSA).
2017 – SESO revamps its institutional and digital identity.