The spice of life! In our IT world, variety is always at our fingertips and bouncing before our eyes. For good or for ill, it is almost impossible to be bored unless you schedule boredom into the day.
Practicing without getting bored can be a challenge for many students. For one thing, they often get into a habit of starting at the beginning of piece and playing to the end, no matter how often we suggest other strategies. And practicing does involve repetition, which can be one step away from the boredom pit.
My first suggestion is to realize that students will probably not come up with clever ways to practice on their own. They need suggestions. One of my favorite suggestions is to make a work copy of an assignment, then cut it into small pieces, maybe four measures segments. Put these pieces into a shoe, a hat, a bag, a box - anything that is handy. Then pull out one segment at a time, and start practicing from there. This can be a great way to test memory as well.
Another suggestion from my book Sensory Tune-ups, is to make a work copy and have the student color it with colored pencils or crayons. This is a way for the student to express feelings about the music as well as showing the teacher what stands out in the score.
Students often need specific direction on what to notice in practicing. Maybe rhythm or harmonies. Maybe movement decisions. Maybe the musical line. Helping students to develop awareness helps them to stay more focused when practicing and therefore less bored. It can also be helpful to remind them that it is fine to leave a piece and work on something else, then come back to the first piece. This process, called interleaving, proves successful for many kinds of learning.
For more ideas on amping up variety in practice, check out the website teachpianotoday.com by Andrea and Trevor Dow. Being willing to try something different can be positive for the teacher as well.
Most experienced teachers have ways to change up the lesson itself. Maybe shifting the order of elements of the lesson, or throwing in a surprise duet to sight-read, or getting up off the bench for some movement explorations. Keep in mind that the brain likes novelty as well as structure.