There are large chunks of wood in the class, including a circular cross section thru a tree trunk. You can use this to show the xylem and the phloem, the vascular cambium, the cork cambium, the phelloderm, and the cork. There are smaller quarter-sections of wood that they can practice on. In one of the drawers is a tablet of papers that has an enlarged, black-and-white picture of a cross section of a tilia (basswood, or woody dicot) stem. I use colored markers and ask questions on that. On the flip chart, there is an entire page covering cell types.
This is often the most difficult lab for the students. Expect to spend a LOT of time explaining the difference between vessel elements and tracheids (one is a straight-shot, copper-plumbing pipe, the other looks like a, well, a bunch of slugs...water can't travel thru them in a straight line but has to zig and zag thru them).
When talking about secondary walls, I use the concept of the walls of a house. For your bedroom, you might have sheetrock walls. That's your typical cellulose wall. Doesn't provide any support, not real strong, but it keeps the stuff in your room in your room. However, for casparian strips or any cell that needs extra protection, there is a second, lignified wall. I tell students that this is like the cinder blocks on the outside of the house. You still have your sheetrock on the inside, but there's an extra layer on the outside that is MUCH thicker and tougher. If you have a corner room, you might have two walls that are sheetrock with an outer covering of brick or cinderblocks, and all four walls with sheetrock. This helps explain the concept of casparian strips. When you're dealing with vessel elements, I explain that the cell's entire purpose is to make a long pipe, and die. That way, you don't have a nucleus and other organelles blocking the path of the water; all that's left is that cinderblock on the outside. An analogy for this is a concrete culvert.....you put your corrugated metal pipe in the ditch, and that's the cellulose wall. Then you pour concrete around it....and it's the concrete that provides most of the strength and almost ALL of the bulk. If they ever want to see how tough that extra wall makes it, bring in some celery and pull the fibers out of it! Those are the vessel elements!