The school Andrew O'Donnell and Max Wall attended in Dublin describes a "day of immense sadness" following the "devastating loss" of two former pupils.
Two teenage boys have died on the Greek island of Ios.
They have been named Andrew O'Donnell and Max Wall, from Ireland.
They completed their studies at St Michael's College secondary school in Dublin this year, which said it was a "day of immense sadness".
The school said Max was a "constant source of positivity" and described Andrew as "popular" and a "committed" footballer.
It said in a statement: "We have been notified of a devastating loss from the class of 2023, with the passing of Max Wall.
"He was extremely popular with staff and students alike and a fantastic supporter of our teams during the various cup campaigns (as well as a great brother to past pupil, Charlie).
"Our thoughts are with Max's family at this awful time and with his friends who have experienced such shocking loss over the last 24 hours."
In an earlier statement, the school said Andrew was "not only a popular classmate and friend but a proud and committed football team member".
Greek police on Sunday night confirmed they were investigating the deaths, which occurred in separate incidents on the Cycladic island. The students were with a larger group from the Ballsbridge secondary school, celebrating the completion of their exams.
A spokesman of the Southern Aegean regional police directorate said Andrew O’Donnell’s body was found by police at around 9.20 am local time on Sunday on rocks in a field outside the island’s main town of Hora. His body showed signs of falling, but it was unclear whether the fall had been from a height.
The spokesman said Max Wall was found unconscious by a member of the public near the island’s port at around 2 pm. The emergency services were informed, and he was transferred to hospital by ambulance, where he was pronounced dead.
