The presentation reports a study done in early 2006 to explore the effects on students' learning of geometry with dynamic geometry software. This was a case study of a class of Secondary 3 students when they were learning the topic "The Properties of Quadrilaterals." The study focused on the design of pre-constructed Sketchpad files and worksheets in the case of exploring the properties of some quadrilaterals. The important elements of the pre-constructed Sketchpad files and worksheets were considered, which include the design principle of the Sketchpad files and the format of worksheets. Students' attitude towards the use of computer in learning geometry was also explored.