It's easy to assess a student's difficulty with navigating scales in progressive tempo framings from quarters to 8th notes to 16ths, etc. as being the result of shortcomings in rhythmic perception, when a larger cosmos of awareness is lacking.
I think immediately of the Eurhythmics course I took at the Oberlin Conservatory, taught by the legendary Inda Howland. It was not a doctrinaire approach to realizing the individual character of rhythms according to the tenets of Jacques Dalcroze. Instead, it was in part an imagery fed environment that supported the motion of the body in understanding the flow of notes as it also nourished relaxed breathing tied to the vocal and movement model. Triplets were expansive, rolling, and unrelenting, never crowded into a narrow space. They had to "breathe" in concert with our organic sense of them. (Think "vowels") To experience the breadth of these notes, we grouped them in a horizontal procession, swaying, and physically ingesting their uniqueness.
In a transition to 16th notes, we realized a new character framing, a different "inner speed motion." Our mentor spoke of "density," unswerving "energy," and lack of inhibition. She referenced "shape," "contour," "freedom" of physical and emotional expression.
If I tried to cram all that I absorbed from my Eurhythmics experience into a piano lesson, it would be a formidable task. Yet, I find myself prompting my students, not just with mental images, but with conducting motions, singing, demonstrating, and opening the piano technique portion of the lesson to a wide universe of personal/physical/musical discovery. (Choreography at the keyboard is a vital ingredient of rhythmic realization, but it's always at the service of what's "natural" or "organic" to the outpouring of notes)
Therefore, a metronome, per se, will not "correct" rhythmic weakness. Instead, an integration of ideas that harnesses the imagination, relaxes the body/mind and opens the student to experimentation and self-analysis, can go a long way to stimulating an awareness of how notes "breathe" in groupings to phrase peaks and resolutions.
A local interaction with an adult student (B minor arpeggios and scales)
My "Rhythm Rehab Lab" centered tutorial that followed a lesson with a pupil in Australia
Original Content: Piano Technique: Working with the character of rhythms