Answer
My high school did not encourage creativity, or it did not encourage diversity.
Work Step by Step
It is not the case that my high school encouraged creativity and diversity.
Let p and q represent the following statements:
p: My high school encouraged creativity.
q: My high school encouraged diversity.
The statement is of the form ~(p ∧ q). An equivalent statement is ∼p v ∼q.
Therefore, the given statement is equivalent to:
My high school did not encourage creativity, or it did not encourage diversity.