Middle school students should have good ______(behave) in daily school life.
The answer to the question is behaviors.
But why use behaviors not behavior?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
Behaviours sounds very strange here. I would use behaviour instead.
Overall this sentence is weirdly structured. Behaviour is not something you usually "have". The sentence is better written as:
Middle school students should behave (well) during daily school life.
Or if you wanted to use behaviour as a noun:
Middle school students should show good behaviour during daily school life.
Other verbs are available instead of "show" such as "exhibit" or "exemplify".