Whole milk should be introduced at one year, not before. There are several reasons for this, but one of the most important is because right now, Bentley (it's Bentley, right?) is getting a lot of his nutrition from the formula. You don't want to replace the formula with something less nutritious until he's getting more of a balanced diet. By one year, you'll have been giving Bentley veggies, fruits, proteins, and starches enough that he won't need to rely on the milk so much. Another reason to hold back on the milk is the chance of triggering a lactose intolerance. You should already have introduced cheese and yogurt to him. These products have less lactose than straight-up milk, so they're a good indicator of whether or not you can expect problems with milk, and they're safe to introduce to kids below one year. But milk is the big one, and more kids are developing the intolerance these days (and I'm sure there's a thousand random reasons why, none of which are important to you right now). Congrats on trying the switch to sippys. It'll start working as soon as Bentley gets used to the new way of drinking. You may want to try switching up sippy styles as well; some kids definitely have a preference. My son likes the kind with straws; he never cared for the other style at all. Unfortunately, I'd already spent a good $25 on sippies before I figured that out! Good luck!