It depends on the context.
The past perfect can be used to show that one event occurred before another event occurred and finished:
I was waiting at the back of the line because I had punched the son of the principal.
If the order of events is clear, we can just use the simple past tense:
I was sent to (wait at) the back of the line because I punched the principal's son.
The before makes clear the order of events, so it becomes optional. British English pulls stronger than American English toward considering the perfect aspect as required or better. Using the perfect also tends to be more formal.
(The son of the principal is also ok, but 's would probably be more common, depending on context and other factors.)
Other examples of finished past events that occurred before other past events styled without use of perfect forms:
He brushed his teeth and went to bed.
She killed her kids and went to prison.
The choices we use depend on many factors, including register.