This experiment involved college students (N=464) working on an authentic learning task (writing an essay) under 3 conditions: no feedback, detailed feedback (perceived by participants to be provided by the course instructor), and detailed feedback (perceived by participants to be computer generated). Additionally, conditions were crossed with 2 factors of grade (receiving grade or not) and praise (receiving praise or not). Detailed feedback specific to individual work was found to be strongly related to student improvement in essay scores, with the influence of grades and praise more complex. Overall, detailed, descriptive feedback was found to be most effective when given alone, unaccompanied by grades or praise. The results have implications for theory and practice of assessment.