Gerard Simons is especially active in the 1920s and 1930s, building churches, schools and houses in the Hague area, such as the Jeroenkerk and schools on Rosseelstraat in Spoorwijk. He is responsible for the renovation and expansion of the schools on the Hekkelaan, Zuid-Oost-Binnensingel, Zwarteweg and the Jozefschool in the Van Beijerenstraat in Voorburg. His style is akin to that of Kropholler. For the Ursula Clinic in Wassenaar, Simons collaborates with H.J.W. Thunnissen and J.H. Hendricks.