It appears that a large number of students were home schooled in 2006 as compared to 1999.
Work Step by Step
This graph is misleading because it is only a 1.2% increase. Graphs using 2 or 3 dimensions tend to make gains or losses look much larger than they actually are. ALso, there are no units on the graphs. A good graphical display of data will have units and will show the zero mark on the graph.