The story begins in January 1964, when a group of young families with school-age children from the area of “Lomas de San Isidro” decided to found a coeducational, secular and bilingual school.

To meet the initial expenses they decided to issue shares, which were underwritten not only by parents of students, but also by the parents of future teachers. In just a couple of months they rented two pieces of land and a small house. Five trams were installed and were remodelled to be used as classrooms. In this way, the school was born in March 1964 with the name "Lomas de San Isidro School", with an enrolment of 75 students.
 
During the first year it was re named.  "Colegio San Marcos", adopting the lion of St. Mark the Evangelist, in its shield.
 
The following year 1000 square meters of the leased land were purchased, and in 1967, the first building of the primary section was built. It had eight classrooms and the heads’ offices. By that time the School already had 108 students. In 1969 the number of students was doubled and taking into account this demand, more than ten classrooms were built.  Two preschool classrooms were added to the primary building.  Some years later the Hall was built.

More than ten years passed (1978) to fulfil another desire of the associate members: to start the secondary level. It began with 22 students in new premises.

In 1982 the first group of secondary students graduated and, in that same year, the school declined the government´s grant.
 
 A sports field in Garin, was purchased in 1984, and the construction of sports facilities began. Each family planted a tree to begin afforestation in the field.
 
In 1986 a neighbouring house was bought on Murature street in which it was decided to install two preschool rooms. In 1987, Elementary and Secondary levels already had two divisions each year. The Kinder level opened an independent building in 1990 with 125 students.

In 1991, with 740 students, three classrooms and sanitary facilities for first grade, a Computer Room for Primary and a central library serving the entire St. Mark’s community were built. Years later a Laboratory and a Computer Science Centre for teachers and students were opened.
 
During 1997/1998 the Hall was extended and equipped with new stage curtains, lights, etc. and the "Conference Room" in its basement was opened. The following year a Computer Lab was added to the whole school and the secondary school building is remodelled, providing it with air conditioning.
 
In 2003 K2 opened. In 2004, to celebrate the fortieth anniversary of its foundation, an interfaith meeting was shared by the seven hundred students, all the staff members, parents, alumni and special guests, reflecting the image and summary of a community committed in the pursuit of cultural and spiritual enrichment.

In 2010 the tram classroom was restored as a school symbol and the adjoining house on Murature  street was bought.