I have purchased too many of these cups, as now my son is addicted to them. They are almost like a bottle to him..but regardless, they always leak. This is not due to any destruction that he is doing to the cup, it's just that they will leak eventually. This is frustrating when you have to clean many spills from things like couches, and beds.
So, the only solution I have found is a look-alike cup, made by another company. It is similar, but the spout is a little differnt. Let me tell you, it works much much better!
I think they are available at Walgreens, for about the same price:)