Efstathiou created the Classroom series in early 2000. The inspiration behind these paintings stems from a school visit during which Efstathiou was invited to hold a talk. As soon as the school bell rang, all the children disappeared from the classroom in a matter of seconds. The room was empty and in a state of chaos, with chairs pulled aside in a disorderly fashion.
The sight of the chairs and school tables in the silent room looked very sculptural and geometric, almost like an installation. Efstathiou instantly followed his instinct and created the Classroom series, which came to be one of his most well-received projects. The colouristic explosion that was brought about by movements of the 20th century, such as Fauvism and German Expressionism, are highly evident in this line of works. Large, heavily coloured surfaces make up Efstathiou's interior spaces, sturdily constructed, and inhabited by deformed figures, loosely sketched in colour. The dominant theme in these pictures is that of the school classroom, in which several, often tiny, student figures are uniformly - one might say, mass-like - portrayed. On the contrary, teachers are extremely tall figures, rendered in the manner of Alberto Giacometti, thus accentuating the awe that is inspired by the often monumentally constructed spaces.