The Eleuterio Derkes Grammar School () is a historic school building in Guayama, Puerto Rico. It was built in 1908, during a period when schools were gaining importance as civic institutions in Puerto Rico. Its simplified Neoclassical design emphasized this shift, and it became a prototype for a generation of school construction on the island. It additionally signifies a transition in construction technologies from wood to concrete. In 1987, architect Jorge Rigau observed that the building had survived in a nearly unaltered state, a rarity among schools of its era.
It was inscribed on the National Register of Historic Places in 1987.