<p>No, you can never tell whether a professor will get tenure. Often, the department itself is surprised when tenure is denied after it recommended it. </p>
<p>There are several stages to tenure review, and all in all, it takes about a year to complete the process. Some professors get fast-tracked for tenure when they come from highly regarded backgrounds --- usually from another school or with substantial research and publications. These profs are generally hired as Associate Professors, but without tenure. (As someone else said, usually Associate Professors have tenure.) Assistant Professors are generally those who are in the first ten years or less of their careers. There are exceptions to this last, but I won't get into it here.</p>
<p>In a nutshell, tenure committees take the following into account: publications (are they numerous? in respected journals? do they reflect innovative scholarly work?), teaching (evaluations, the number of grad students, if applicable, and the quality of the grad student work), research (this ties into publications for the humanities and grant money for the sciences and some of the social sciences), outside recommendations from experts in the field, and service to the university (committee work, advising, all the soft stuff that students never see). Students are rarely in the position of being able to evaluate the quality of research as compared to a national pool, of publications, and of service. That's why you can't predict success, although you <em>can</em> increase the odds by being another student.</p>
<p>If you are in the sciences AND an assistant professor supports you, you can be relatively certain that the prof has grant money, which is usually tied to quality research.</p>