This toy is a disappointment, the kit is overpriced for what it contains & the function of the rocket is terrible. Building the kit went fine & is enjoyable (which is half the reason to buy kits such as these) & the theory of operation is sound. The problem we had with the rocket is the stopper pops out just as soon as you set it down thus there is no time for pressure to build and the thing just goes about 10 feet into the air. If I try to tighten the stopper it slips out of the bottle opening again & again. I'm going to try to roughen up the bottle opening & the rubber stopper (or try a different stopper) to see if we can get it to stay in place - if this works the rocket should fly much better.