Do many parents spank an 18 year old who has done something wrong? No, because spanking is no longer effective, reasoning works much better.
So if you want to modify behavior you have to understand the subject of your "experiment" and chose the best technique for the circumstances.
When you train a dog one of the rules is to deliver the punishment immediately after the wrongdoing. The dog poops in the kitchen, let the dog know immediately. Why? Because the dog has a limited capacity to make cause-effect connections so the trying to explain to the dog, a day later, that you disapprove of him pooping in your kitchen is just going to confuse the dog.
Well, with a young child, simply because they parrot back to you what you've explained to them doesn't mean that their brain is now guiding and filtering their behavior and operationalizing this new rule you've given them. There's a deeper, more primitive brain at work, still dominant, and it takes maturation to develop the rational part of the brain.