Imagine if your child only wrote or practiced math twice a week? The result would be terrible! The same thing applies to an instrument. That is why they MUST practice 3 or more days at home. The more they practice, even 10 minutes every day, the faster they will see results.
What else can you do? Listen to them at least once a week, if not more. Make sure they tell you what their goals are and what they learned in class. Have them show you their music and what they learned about it in class.
What else? Invest in private lessons if you can. Nothing replaces one on one attention in music. Learning as very complex skill in a large group can be overwhelming for many students. Even a few lessons in the beginning and over the summer can make an amazing difference!
Check out the videos page for some tips for your child. Be positive and encouraging! They will be playing confidently before you know it!