Hi S.:
The problem might be the formula and not the sippy cup. All four of my breastfed babies couldn't stand the stuff and we never had any luck getting them to take it (or even breastmilk from a bottle, for that matter). I'm trying to think back, but for my kids, 9 months was a bit early on getting them to take a sippy cup, but when I introduced it to them, I usually removed the valve - it's a bit messy, but if they're not used to it (or to a bottle) it seemed to help. Eventually we'd be able to put the valve in - but that's if they Wanted what was in the sippy cup.
Take care,
M.
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