Here are my suggestions for summer practice:
1. Organize. How is your practice environment? Summer is a great time to change things up, but make sure that you keep track of things like lesson times, and when/if practice is happening at home. You might have to be creative, but make sure you have a plan for your daily routine with a good time to practice included.
2. Journal. Write down questions, goals, your favorite pieces from CDs or performances that you want to work towards. Sometimes, having less stress from school-year commitments gives you the freedom to think about long-term dreams. If you have a younger child taking lessons, take them to the library to find a violin CD to listen to and write down the name of the violinist and any favorite pieces in the journal. Or, have the child make a list of 'famous violinists' that they see in local concerts, on TV or internet, and on CDs.
Also, in the journal write down the dates that you practice, and any other details that are important. It's good for a younger student just to have a visual record of how many days they practice, and they can put a sticker or picture in lieu of written notes.
3. Review, review, review. Get a good Suzuki review chart---for an advanced player, make a system to play all your scales and etudes regularly, one key per day, etc. AND you have to play old repertoire that is technically easy for you. It is the best way to beat performance nerves, build a relaxed technique and a rich, full, personalized tone.