A haul is a pull of line through the guides during the casting stroke, and in a double haul the line hand returns towards the rod hand during the pause. Teach it that way and the explanation falls into place: the student is timing one thing, not two.

The model most instructors use is start with the start and finish with the finish: the haul begins as the stroke begins, ends as the stroke ends, and the hauling hand mirrors the rod hand. That is a teaching cue built on the definition, not a separate rule to test the student against.

• Give the cue in stroke terms. Students can already feel the start of the stroke and the stop, so tie the haul to those events rather than to a count.
• Make them watch it. Look at the hauling hand while casting; video shows when the haul starts and how long it is.
• Build the feel. Overload the fly rod to help with the feel of the double haul, and use the Horizontal Casting Drill, which the guide lists for practising and teaching the double haul.
• Keep it smooth, not forceful, and haul on every casting stroke, including the pick-up.
• Teach one stroke first. A single haul is a pull during either the forward or the back stroke, so start with one stroke and add the return in the pause once the pull is smooth.

Source

From Task 14 and the learning-styles section of the CI Study Guide (2025) (PDF); terms from the FFI Fly Casting Definitions (Hauling, Casting Stroke). See also Task 14, double haul.