I include in my syllabus a "re-submittal policy" that allows students to re-submit any ON TIME work for regrading if they wish. This has had several benefits: First, if they misunderstood part of the assignment, they get a second chance at it with more clarity. Secondly, correcting your own mistakes has proven to be valuable for learning. This does create some additional work for me as the instructor, but we generally have small classes, and this has been manageable. This is not allowed for tests, of course, but for project-based assignments that are more creative in nature.