@randaroo, I had that issue. It took me about a month and a half. I wanted to introduce it early and it has seemed to stick. This morning was the first time he drank all of it with no issues. He used to scream because he couldn't get his milk out but he finally figured out that it's different than his bottle.

Mine puts in his mouth, pulls it out, looks at it all crazy, and repeats this process for 30 minutes. Doesnt drink a drop!