It seems to me that there are two problems with ornaments: technical and visual. The technicalIt is not just that students can't get their fingers around ornaments on the piano - although the speed and delicacy is often a problem; I think that many players are confused when they shouldn't play the note printed (e.g. in baroque trills, they have to start on the upper auxiliary - they see a C and have to play D first).
Also, there is the problem of remembering what the different signs mean. Even intermediate players don't come across ornament signs very often. In fact, it's not until they have to learn them for ABRSM Grade 5 Theory, that they do actually learn them. But, without the context of using ornaments, it can be difficult to remember them. I've written a little piece this Summer - piece is perhaps too grand a word - but it is more than a table!
I've given this piece the subtitle Explication, because that is what Bach called the table of ornaments which he wrote in the preface of the Clavierbüchlein vor Wilhelm Friedemann Bach (see picture).
For Grade 5 theory (ABRSM), the student is asked to recognise ornaments (i.e. name them), and also be able to replace a written-out ornament with the appropriate sign.