My school currently does not allow for extra credit. However, I found that students were showing up late for classes a lot and not reading the material, so I created reading quizzes. I give a short quiz on the reading material at the beginning of each class before we go over the material. If they are not there for it, they do not get the opportunity to take the quiz. If they are there, they take the quiz and if the cumulative grade on these reading quizzes at the end of the term is higher than one quiz grade, it replaces the quiz. If it is lower, the reading quiz does not work against them but is used as a study tool to see what they need to focus on for the main quizzes and tests. Since implementing this, students come to class on time and read the assignment more often.