Since this was posted in June, did they eventually learn? I'm coming across a similar problem now. My first girl started laying at 16 weeks. Imagine my surprise, and we hadn't yet gotten the nest boxes up. Since then, everyone else has started laying in the nest boxes. The one who didn't lay in the nest box still doesn't, but she lays off to the side out of the way, and it's not a huge problem.
However, just today I found two eggs not only on the floor but UNDER the roost...yuk. They were small and soft, and therefore I suspect they are coming from hens just starting to lay. I have no idea why they chose there, but I want to stop that before it becomes a bad habit!
I have 15 pullets but they are all starting laying at various times. I may start a separate post for this question, but was wondering what happened in your case.