resulted

[diogerepus]

How can I explain why "resulted" is used in the blank, instead of "results"?

When we are not fully prepared for the changes in the exam system, chaos resulted.

 

[Kevman]

I don't think you can explain it. I think results is the right word. It should be in the present tense in agreement with are.

 

[bibliolept]

Correct. "Are" is present tense, as is "results".

The alternative is, then: "When we were not fully prepared for the changes in the exam system chaos resulted."

 

[padredeocho]

How can I explain why "resulted" is used in the blank, instead of "results"?

Better:
Because we were not fully prepared for the changes in the exam system, chaos resulted.