I have taught the course where CS undergrads tackle proving for many years. It has not been my experience that for those who have difficulty the stumbling bloc

I have taught the course where CS undergrads tackle proving for many years. It has not been my experience that for those who have difficulty the stumbling block lies in making sure that their arguments are formalizable. This may have to do with my institution and my students (or perhaps with me) but I find that 30%-ish of them just do not have a turn for mathematics or proving, at all. Just as I do not have a turn for graphic design and no amount of effort moving things around in the GIMP seems to help, these folks do not get even the simplest exercises in Epp or Rosen. Even when the other 70%-ish are very ready to go on, there is a core that will not get those questions on the exam no matter how much time we devote to the topic. (These folks, as far as I can tell and I've been doing this since 1990, go on to solid careers.)