I note hand positions and respond something like, “Those are pancake hands. That’s for breakfast, not for piano playing.” It’s funny but makes a point.
An interesting way to work on scales is to try to balance a deck of cards on the hand while playing. This requires finger crossing without tipping the cards. It makes scale drills a game.
When a student is guessing at a note and looks up at me for a “yes or no,” I say, “Do I have notes on my face? If I do, I’d better go wash my face.” They laugh and realize that I’m not going to give away a chance for them to figure it out instead of guess. Guessing will never create a proficient note reader.