I used an object lesson and quiz to teach the concept of physical/spiritual cleanliness.  Last night I took an egg and blew the egg out of the shell (if you haven't done this before, it's easy; make a hole in both ends of the egg with a pin or small nail, then blow through one end.  The egg yolk and white will come out the other.  You may have to puncture the yolk, too).

After the shell was empty, I  partially filled it with chocolate syrup and covered the holes with small pieces of white tape.  I used a syringe to fill it, but you could slightly enlarge the hole and drizzle it in.   We discussed Mark 7:1-23, and I used the quotes to talk about inward/ outward righteousness.  I held up the egg to discuss how something can appear to be pure and clean on the outside, then broke the egg and poured out the chocolate syrup (into a handy bowl).  We discussed that what really matters is what is inside, not just the outside appearance which can be deceiving.  I asked them to think about how much time they spent preparing their outside appearances for school today, and challenged them to spend the same amount of time today on prayer, scripture study, or just thinking about their lives and what changes need to be made so that they can have both clean hands (righteous actions) AND clean hearts (righteous intents, thoughts).