Recent years have seen widespread adoption of automatic grading of physics homework problems. Although first-generation homework management systems provide feedback and assign scores based only on the answers, problem-solving performance on exams seems to be no worse for students using these systems than for those who receive detailed comments from manually graded homework. Apparently immediate feedback, which encourages students to continue to work on a problem until they "get it right," is as effective as detailed, but delayed, comments on a complete written solution. Second-generation homework systems should combine the two approaches by using immediate feedback in grading complete solutions.