We heated up the milk to the correct temperature, added the salt and some lemon juice (citric acid) and the rennet, and waited for the curd to form. A couple of minutes later, no change. Five minutes, no change. Ten minutes (at this point you're supposed to have a nice solid curd), no change. Twenty minutes, no change. The curd was nowhere to be found. We figured that the milk we bought was "ultra-pasteurised", which means it was heated to a somewhat higher temperature than that of normal pasteurisation. This makes the shelf life longer, but it breaks down the fragile proteins in milk and makes it completely unsuitable for cheesemaking.
Sure enough, when we called the milk company the next day they confirmed it was ultra-pasteurised. So, we'll need to find some whole milk that hasn't been heat-treated to oblivion if we're actually going to be successful. Disappointing, but at least we were out only a few dollars for the milk.