The 70-year-old royal, who first visited the school in 2007, took a tour of a newly renovated building.
The Prince of Wales also unveiled a new plaque to mark the special occasion.
Charles appeared to enjoy the engagement, smiling and laughing as he chatted to students about their work.
The engagement comes just days after Charles and Camilla released their Christmas card.
The lovely picture shows the couple sitting on a bench looking adoringly at each other in the gardens of Clarence House.