Interpretation:

The low p-value thus rejects the null hypothesis that the underlying distribution is a normal distribution.
I now want to check if there is a difference in the distribution of the scores from schools which have  >0 outlets with >15 ppb lead contamination and those which have 0 outlets with > 15 ppb lead contamination.
Since the overall distribution is not parametric, I make use of the Mann Whitney U test to compare these two distributions: