Four forms of Rhythmical Movement:

There are four main divisions of rhythmical purpose or attention in playing:

1. Key-movement the swing of the key downwards, towards Tone-emission.
2. The group-sensing of notes in a quick passage, as groups of notes always leading towards each next pulse or beat.
3. The growth or progression of the Phrase-unit towards its rhythmical climax near the end of the phrase, and
4. The movement or progression of the piece as a Whole towards its climax.

The challenge during practice and performance is to continually pay attention to the motions executed and sound produced. Either musically or pianistically, no matter whether you are a beginner or an experienced artist.

To cultivate the student's awareness of alignment of the fingers with the flexors and extensors of the forearm, I would have the student drop a single finger on a book to experience that after the finger makes contact with the surface, the hand, wrist forearm do not continue with an extra downward exertion.
We comparing this sensation to walking, our foot makes contact with the floor and we do not continue dropping our knees and legs, or rolling over our ankles. You can have fun with helping a student develop this connection by using whatever images that are effective. To offer a student the sensation of the wrist being connected to the hand and forearm will enable his awareness of hand-exertion.