In lieu of the on-going piano examinations and my experience in conducting Sight-Reading classes for students, many students find developing a good sense of rhythm is one of the most challenging part of playing the piano. Some piano teachers might also find developing a good sense of rhythm in their students is also just as challenging for a teacher. Rhythm is not something that must be maintained as the student progresses to more advanced rhythms and irregular meters. It is something that must be developed and not something that is possessed overnight.
I believe that there at least 3 components to having and developing a somewhat "good sense of rhythm":
Thus when a student has a rhythmic problem in one of the pieces, it is good to identify which of these 3 components might be lacking. Many teachers would solves these issues quite differently.
Hence in my sight-reading classes, I provide the opportunity to develop a good sense of rhythm in the students. I give the students activities involving tapping, clapping with one hand or both which develops their sense of beat (see point no. 1). Soon after, students can begin creating various rhythms within the steady tempo and understand how subdivisions of note values work.
I will give them different rhythmic activities within a given time-signatures. Pretty soon, they are able to absorb and feel what these meters sound and feel like. All these are great foundations for dealing with pieces, and they use these and apply them to future pieces.
There are certainly many ways to develop good sense of rhythm in students, but the most important of all is to show students that rhythm can be fun and helpful in their piano playing!