Rotate tick labels for seaborn barplot

You need a different method call, namely .set_rotation for each ticklables. Since you already have the ticklabels, just change their rotations:

for item in by_school.get_xticklabels():
    item.set_rotation(45)

barplot returns a matplotlib.axes object (as of seaborn 0.6.0), therefore you have to rotate the labels this way. In other cases, when the method returns a FacetGrid object, refer to Rotate label text in seaborn factorplot

You can rotate seaborn xticks like so:

sns.barplot(x='Organization Name', y='Score', data=df)

plt.xticks(rotation=70)
plt.tight_layout()

Use the following code statement:

by_school.set_xticklabels(by_school.get_xticklabels(), 
                          rotation=90, 
                          horizontalalignment='right')