Trying to rotate child independently of parent...

I have a child object with these bits in the script...

 Quaternion targetRotation = new Quaternion();
 Quaternion currentRotation = new Quaternion();

 void Start() {
     currentRotation = this.transform.rotation;
     targetRotation = this.transform.rotation;
 }
 
 void LateUpdate() {
     targetRotation = this.transform.parent.rotation;
     currentRotation = Quaternion.Lerp(currentRotation, targetRotation, rotationSpeed * Time.deltaTime);
     this.transform.rotation = currentRotation;
 }

As far as I know, the child should rotate at a different speed than the parent, and indeed, when I Debug.Log the current and target rotations each frame, I can see the current interpolate to the target slowly. However, when rendering, I don't see this.

I'm a bit befuddled.