I'm trying to gather info and statistics on how exams/tests in schools negatively impact creativity, does anyone have any theories/facts etc. that might help please?

It totally depends on the subject.

Science/Math isn't about creativity ... It's about processes and facts.

English ... Tests can encourage creativity, depending on the class subject.  I mean, is it a spelling/grammar test - or creative writing?

Same with Arts and Music.  Is the test about how a painting was done, or how to read sheet music ... Or is it to create a painting or piece of music?