Secondary mathematics educators and government officials in many countries are actively engaged in the investigation of the inclusion of Computer Algebra System (CAS) calculators in the high school curriculum. Active Asian countries or regions include Singapore, Australia and New Zealand. Using CASIO ClassPad 300+, this workshop aims at giving Hong Kong teachers an overview and some basic skills in Main Algebra and Geometry Functions and Applications of CAS calculator. Hong Kong classroom examples, exercises and local public examination questions will be used to illustrate the power of this new technology. Finally, simple lesson and assessment design will be shown as examples for the building of CASTLE (CAS Teaching and Learning Environment) in local classrooms. Cantonese will be used as medium of instruction.