The Operating System is a very complex program that runs on our computer (probably the most complex …). It is difficult to comprehend the diversity of its operations, let alone – teach it. Second/Third year students with beginner programming skills are overwhelmed by the OS size and its multiple tasks. This paper is focused on how-to better teach the operation of the OS Scheduler that manages the user’s processes. The scheduler tasks are: create the process, load it into memory, allocate CPU time-slices for its execution, handle keyboard clicks and menu selection, swap the process in and out of memory, and instructs the devices to satisfy IO requests. The question is: “how can we give the students hands-on experience on the scheduler operation? “ Obviously, a few slides and a state-machine diagram, is not enough. The answer consists of: explanation (slides), simulation and an exercise. The simulation package includes two simulators (two levels of complexity) each running userdesigned scenarios. The 1 st simulator (A) is a simple Round-Robin scheduler that is easy to follow. The 2 nd simulator (B) comes much closer to a real OS scheduler (with all its complexity); as such it is very difficult for the student to understand, unless they play with Simulator-A first. The exercise goal is to write a “scheduler” that allocates the “CPU” time among ten “Processes” each doing a “long” task. The exercise can be accomplished by 2 nd -3 rd year students.