In 1823 the Latin school became a "Progymnasium", meaning that a more encompassing list of subjects was taught. The last Franciscan headmaster died in 1837 and in 1898 the school was made a full Gymnasium. Petrinum subsequently moved to a new building in 1902 and in 1904 the first Abitur exam was conducted at the school now officially named “Catholic Gymnasium (with compensatory education in Greek) at Dorsten”. During the Occupation of the Ruhr in 1923 the school building served as headquarters for Belgian troops, which meant that teaching had to take place in another building.