Okay, this lesson doesn't really require cupcakes but they can help! Before you ever teach the students the mathematical definition and how to use the Distributive Property you need to make sure they have an everyday definition and understanding of the word Distribute.
What does it mean to distribute something. I always use cupcakes as an example (and yes, I have brought them in to demonstrate). I ask the class would it be fair if I only passed out my cupcakes to the first row of students?
Of course they emphatically say no (unless they were in the first row). I ask them, why not?
They tell me because to be fair I need to pass them out to everyone. I agree with them and then go into the mathematical use of the Distributive property.
If I only multiply or distribute the x to the "first term" (referring back to the first row of students) in x(a+b). I would get
ax + b which wouldn't be fair to the "second term" or in this case b. So, to be fair we would have to Distribute the x to both the a and the b to get ax+bx.
There you have it! They will never make the most common mistake with the Distributive Property ever again! Then when I teach them to distribute multiple terms to multiple terms like when multiplying two binomial terms together. I refer back to the cup cakes and ask if I brought in Cupcakes and Milk would it be fair to only pass one out to the first row and one to the second or both to the first row and not the second.
The easiest way to get them to understand the Distributive Property is to get them to understand it has to be fair across the board for all things being distributed and all thing receiving the distribution.