“Can {child_name} drink from an open cup on {his_her} own, without too much spilling?”
Follow-up: “Is it most meals, or still mainly a sippy cup?”
Not yet
Prefers bottle or sippy, spills heavily from an open cup
Emerging
Drinks from an open cup with a helping hand
Developing
Drinks from an open cup {him_her}self with some spills
Secure
Drinks competently from an open cup with minimal spilling
Half-full cups and little frequent sips are the easiest way to practise.