Adams developed slowly, and did not expand beyond its original building, now known as "Big School", until the turn of the last century when "Main School" (also known as the "S-Block") was built in the 1920s. Over the course of the next 90 years Adams' expanded rapidly, acquiring a number of buildings on Lower Bar in Newport for use as boarding houses; this in turn greatly expanded the school's town centre site. In the 1960s a new science block, connected to Main School was built, whilst a senior boarding master's house was created on land adjacent to Big School. During this period the school also acquired a new gymnasium, which was subsequently converted into a theatre in the mid-2000s.