If Massachusetts Charter Schools and non-Charter Schools had the same rates of high school enrollment decline, we would expect some natural variability between the two systems. That is, if the two systems had the same rate of enrollment declines, sometimes Charters would have a higher rate of high school enrollment decline, sometimes a lower rate that would average out over time unless something really unlikely happened. Looking at the enrollment declines for hundreds of traditional districts and dozens of Charter districts over a several year period, we have enough data points to be confident that our data means something. With the removal of one Charter school outlier, the dramatic difference between enrollment declines of Charters and non-Charters, a standard deviation of about 2.5 and a P value of .0082, means that there is a stunningly small chance that the much larger enrollment declines in Charter high schools compared to District high schools happened just by chance. That means it is very likely that the excessive enrollment declines at Charter High Schools happened for a reason and as policy makers, it is crucial for us to understand that reason or those reasons before we increase the number of Charters in the state.