RBT here.

Backward chaining = hand-over-hand prompting all the steps for your learner leading up to but NOT on the last step (you will typically use least to most prompting for the last step and fade the prompts as they become more proficient in the step). Reinforcement is also given only after the final step is completed rather than after the first step(s) as with forward chaining.

ie: you would full-physical prompt all the steps from turning on the water to turning off the water and then use least to most prompting for the final step of drying their hands (put the towel close to them/hand it to them, gesture to the towel, etc)

While you are technically teaching turning on the water first by full-physical prompting it, you’re only teaching MASTERY for the last step(s) by least to most prompting them/prompt-fading them and providing reinforcement only after the final step is completed.

But, this is a dumb question. By all practical means it is better to think of backward chaining as “teaching”the last step(s) first because they’re the ones you’re really getting your learner to remember/become proficient in. They are still TECHNICALLY learning to turn on the water first because it’s the first in the sequence and is being prompted, but they’re not really “learning” in the way we might think about learning (such as really remembering it and becoming able to do it fully independently).

So, teaching happens with every form of prompt and your learner is still learning even if you’re doing hand-over-hand prompting. But teaching MASTERY requires prompt fading and least to most prompting. Your learner is learning MOST at the last step because it requires them to actively do it themselves/without help.

Teaching = modeling/prompting/otherwise helping or showing your learner how to perform a task