So let's apply it to piano...you can't very well remove some of the keys from a piano, (although we all would like to do that every once in a while!)
What can we remove? We can remove different layers of concepts during practice or introduction of a new unit. For example, if the student is learning a new rhythm, then take away the keys and pat the rhythm on the table or his lap. If your student is learning a new interval, like a 6th or 7th, then as they learn the hand position, take away the rhythm until mastery of new concept is achieved. Once achieved, then slowly the layers can be added back on. The goal is for the student to reach different levels of success at each practice and each lesson.