In 1906, the school purchased a property, "Roxeth" (now Henty House), a small distance to the south of the church, on the corner of Wellington Street and Charles Street. Trinity quickly built Arnold Hall, the first classroom block, completing it the next year. In the same year, Trinity was registered as a public school of the Church of England. The school leased "Molina", a property on the other side of Charles Street and the site of the former Kew High School which is now further to the north, in 1908. In 1909, the school built a science laboratory beside Arnold Hall.