This paper presents a Simulation-based interactive Virtual ClassRoom web system (SVCR: www.vclasie.com) powered by the state-of-the-art cloud computing technology from Google SVCR integrates popular free open-source math, science and engineering simulations and provides functions such as secure user access control and management of courses, assignments and grading. This system allows customized course and lesson development and supports teacher and student account management. The simulation programs are built into a single database to be indexed for easy browsing and keyword search and can be downloaded and run with Java support from our web site. This system has an intuitive and user-friendly interface to allow a quick and easy transition to this system for most users. Teachers can create five types of popular assessment questions namely true or false, multiple choice, matching, word bank, and free answer questions. The system can be viewed in both English and Spanish. In addition, the system can automatically grade assignments--with the exception of free answer questions--to reduce the teacher's workload. Clouding computing technology driven by the Google App Engine is used to achieve scalability when the system is under high access demand. (Contains 18 figures.)