At my daughter's Freshman class orientation, the student's began chanting "Chocolate Cake, Chocolate Cake, it's the only way to erase your mistake!"
HQT Cards are the way to "erase your mistake" in my classroom.
At the beginning of each grading period I give my students two or three HQT Cards. They can use these cards to either turn in a missing assignment or re-take a test or quiz.
The fact that they have only two or three cards adds enough weight to help ensure that they will take the time to go back and LEARN the material that they are missing. Most students are not willing to spend their card re-taking a test on which they are not prepared to score well.
Every has a bad day. HQT Cards are a great way of giving your students an opportunity to "erase" their mistake.
One a side note: the image used on the HQT card is a tesseract. I wait until the end of the year and spend a day discussing dimensions and introducing the tesseract (or hypercube). When the kids start asking what a tesseract looks like, I tell them that they have been carrying one around with them all year long :)