Hi S.,
Both my children had trouble taking a sippy cup. I think they liked the "instant gratification" from the bottle and were not willing to work at sucking on the sippy cup to open the valve.
I got those "Take-N-Toss" disposable cups that come 4-6 in a pack for about $4. It is just an inexpensive cup with a snap on lid with a spout that has about 4 holes for the liquid to come out. No spout to have to open, but that means the liquid comes out fast.
Both took to the Take-N-Toss no problem. I think because the fluid came out with minimal work. From there, they began sucking on the spout and then learned to suck on a regular sippy cup. I did watch them closely for the first few days since the liquid does come out so fast, I was worried they would choke. A few times they did get a big gulp of liquid, but they coughed and learned to adjust their sip. You also have to watch them dropping it on the floor, because it does spill out fast since no valve.
My daughter gave up the bottle no problem at 12 months. My son is now 14 months and still wants a bottle before bed and at 2 am when he wakes up for a snack (yes, I still cave in to that habit - any suggestions on breaking that??). He used to only take the sippy at meals and insist on a bottle for snack, so we are making progress. If only I can get rid of his need for night feedings and the need to be held while going to sleep!
Good luck!
V.