Quizlet has been used by many teachers and students to create flashcards for students to study. You can use it to differentiate instruction in a couple of different ways. The first is to create a list based on your topic and have students login and join your classroom. You can watch their performance with the given list. You know where you need to revisit in future lessons. You can also create different groups with different lists. If students need a shorter spelling list, assign them a different list from another student and see how they perform. This would also work for students who need more challenging words.