Stols, Gerrit Hendrikus; Ferreira, Ronel; Pelser, A.; Olivier, W.A.; Van der Merwe, Adele; De Villiers, Charl Johannes; Venter, S.N. (Stephanus Nicolaas)(Education Association of South Africa, 2015-11)
Stols, Gerrit Hendrikus; Kriek, Jeanne; Ogbonnaya, Ugorji Iheanachor(Southern African Association for Research in Mathematics, Science and Technology Education, 2008)