After introducing the topic of mixed numbers and showing the class what they look like, write a mixed number on the board that uses like fractions. Subtract a mixed number with a like fraction that is larger than the fraction in the first mixed number. The size of the fraction will depend on what kind of food you choose to use as an example. At this point, if you were using pizza as an example, reveal several pizza boxes that are holding cheese pizzas. Gather the students around and create the first mixed number using pizza slices. Show them how to subtract the second by removing exactly that many slices. Do this several times before finishing the lesson by letting the kids eat the pizza.
To ensure that the whole class is paying attention, use all the students to make a large mixed number. As an example, turn 31 students into three wholes and four-ninths by creating three tightly clustered groups of nine students and a fractional group of four. Clear the floor so that they can stand in separate groups. Use them instead of the blackboard to do the problems. Eventually, you can appoint student leaders and tell them to subtract different mixed numbers correctly.
Permit cooperative learning by forming teams out of the students. Do this after the first few assignments so that you can make properly assembled groups which each contain advanced students and struggling learners. Give each group identical worksheets filled with mixed number subtraction problems. Award prizes to each team whenever they manage to finish the problems.
Once the students have performed a lot of work in this area, assign a competition day. Put students in teams to play games that resemble popular television shows, such as Who Wants To Be A Millionaire or Family Feud. In the case of the former, students can use lifelines and even make calls on their cell phones to get assistance.