Practise is one of the most important steps in learning the art of computer programming. Unfortunately, human grading of programming assignments is a tedious and error-prone task, a problem compounded by the large enrolments of many programming courses. As a result, students in such courses tend to be given fewer programming assignments than should be ideally given. One solution to this problem is to automate the grading process such that students can electronically submit their programming assignments and receive instant feedback. This paper studies the implementation of one such automated grading system, called the Online Judge, in the School of Computing of the National University of Singapore for a compulsory first-year course that teaches basic programming techniques with over 700 students, describing the student reactions and behavior as well as the difficulties encountered. The Online Judge was also successfully employed for an advanced undergraduate course and an introductory high school course.