Nicholas Urfe, The main character in The Magus, was teaching English at Lord Byron school on Phraxos. While there is no such school on Spetses, there is the Anargyrios and Korgialenios School for boys where Fowles himself worked as the English master in 1951 - 1953.

This is how Nicholas describes the school in the novel: “The other (eyesore), equally at odds with the landscape, stood on the outskirts of the village and dwarfed the cottages around it: a dauntingly long building several storeys high and reminiscent, in spite of its ornate Corinthian facade, of a factory – a likeness more than just visually apt, as I was to discover”. Whether or not the Anargyrios and Korgialenios School in the outskirts of Spetses town is an “eyesore” on the island or not, is up to you to decide. In any case, the place is definitely worth visiting for Fowels’ fans.

The school itself has an interesting story. It was founded in 1927 and named after its benefactors Sotirios Anargyrios and Marinos Korgialeneios. Sotirios Anargyros was born in Spetses in 1849 to a wealthy and powerful family. After many years of traveling, he settled in America in 1883 where he set up a cigarette manufacturing unit. He later sold the company and returned to Spetses where he lived until his death in 1918. The Anargyrios Mansion is a remarkable Neoclassical building and was used as part of the school complex which also housed a theater and sports facilities.
Together with businessman Marinos Korgialenios from Kefalonia, Sotirios Anargyros envisioned an educational institution that would educate and groom the leaders for the emerging modern Greek society. Their vision converged with the efforts of the prominent politician of the times, Eleftherios Venizelos, for educational reform. The school was designed and operated on the model of the English Public Schools Eton and Harrow and provided humanistic education aspiring to develop the “Universal Man”. When the school originally opened, it had only 4 students but over time it had produced many prominent graduates.

Sources: www.greeka.com, https://www.febs-lipids.org/Spetses2016/venue/anargyrios-and-korgialenios-school-of-spetses