The purpose of this study is to investigate the effects of applications created using a web-based 3D design environment on the spatial visualisation and mental rotation abilities of secondary school students. A total of 63 school students from the sixth grade participated in the study. The researchers applied a mixed research method including both quantitative and qualitative measures. The Spatial Visualisation Test, Mental Rotation Test, and Santa Barbara Solids Test, which concurrently measure spatial orientation and spatial relations, were used as tools to measure the different components of spatial ability prior to and after the treatment application. Following the treatment, a focus group interview using structured questions was conducted. A statistically significant difference showed an increase in all three test scores of the students; also, the students stated that they were satisfied with being able to design and create something new.