I am not a teacher.
Yes, there is a difference.
"Go straight ahead" is a meaningful direction, easily understood relative to the starting position and the way the person (or vehicle) is facing.
"Go straight" is incomplete. It leaves unanswered the question "in which direction?" If it were accompanied by hand waving or pointing it would probably be understood, but it lacks information.
Is "Go straight ahead" similar to "go straight forward"?
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