Some important dates in CGS history include:
September 1973: Costeas-Geitonas School opens its doors with 330 students in Marousi.
September 1981: Inauguration of new school premises in Pallini, Attiki.
August 1993: CGS becomes an official University of London GCE Test Centre.
September 1994: Establishment of the International Baccalaureate Diploma Programme.
June 2003: Inauguration of the Athletic & Cultural Centre, facilities include soccer field, tennis court, volleyball court, basketball court, handball court, amphitheatre, experimental sciences, laboratories, classrooms with interactive technology.
January 2005: Re-establishment of Alumni Association with over 4,000 active members to date.
September 2005: Establishment of the Pre-IB Programme for Grade 10 students interested in pursuing the IB Diploma Programme.
September 2007: Establishment of the International Baccalaureate’s Primary Years Programme (IB PYP) for students between the ages of 3 and12 with Greek as the primary language of instruction and English as the secondary language of instruction.
January 2009: CGS is authorised by the Educational Testing Service (ETS) as an official examination centre for the SAT, PSAT and AP.
October 2009: Establishment of Juventus Soccer Schools, Soccer Academy with exclusive cooperation of Juventus FC.
December 2009: Harvard Graduate School of Education Professional Development Training Seminars for Primary Level teachers.