So we've tried sippy cups and all that.
You can do them one of two ways: one which allows the liquid to pour freely, or the other which has a stopper so the kid really has to suck to get the liquid out.
Frankly the first one is a nightmare because, despite the small opening, juice gets everywhere, and the second one doesn't really teach anything because they have to suck, and the point is to get them to tilt the cup upwards, etc.
Hence our solution, which Matt finally got last weekend.
The straw.
Last weekend he figured out, thanks to a Maggie Moo's Strawberry Cheesecake milkshake, how to suck through a straw.
This past weekend he figured out how to both suck through the straw and hold the cup himself.
Progress is always good.