In 1991, Castle Park merged with Brook House. To reflect the merger and retain something of the heritage of Brook House, a green stripe was incorporated into the Castle Park tie and green stripes into the rugby shirt. Furthermore, what had been Matthews House, became Ross House (Ross was the founder of Brook House).
New changing rooms and three upstairs classrooms were erected in 1994.
Boarding ended in 1998.
In 1999, the Parker Library opened, named after Roy Parker who had been a master at Castle Park in the 1930s and then again in the 1970s until his retirement in 1990.