I have taught perspective drawing for years to 5th graders, partly because of the same reasons already mentioned by others on this listserve. I use a slightly different approach to the problem. I have developed a 9-step process of teaching 2 point perspective that breaks down each step into simple increments. I have laid the steps out on the computer and printed them out on a legal sized sheet of paper, which I duplicate and give to each student. The objective of the project is to construct a house using the steps, then go back in and change the basic house by adding embellishments using the vanishing points and horizon line. The students are required to make as
elaborate a scene as possible using a combination of freehand and perspective-based objects. This is an immensly popular project, and the students are allowed to take home the hand out for practice at home. I have several students returning to school with drawings done outside of class using these. I find that 5th graders have a deep seated need to make things look real, and this method is a great tool for helping them achieve this.
Hope this helps,