I highly recommend Nuby cups to help in the transition. One type of them you can get are like sippy cups where the spout is shaped the same, but it's made of latex like a bottle nipple. You can get them lots of places but I see them most at Wal-Mart. This helped my dd greatly. We used those for milk and regular sippies for water until I thought she was doing well enough with the regular sippies and then switched her to the regular ones for milk as well. She never had any issues with the transition so I hope this helps! And yes, my dd drank slightly less, but she loves her milk so it wasn't much less. I do know that others reduced quite a bit though. She doesn't drink near as much now as she did when she was younger (she's almost 2 now), but she used to almost finish a 9 ounce cup 3 times a day. HTH