Make sure your child is not tired or hungry so that he or she can focus all attention on learning. Also try to keep the lessons consistent with what is being learned in school. A quick chat with the teacher or signing up for an online newsletter from the classroom are ways to keep tabs on the lesson plans.
These are basically digital versions (like ebooks) of worksheets that can be bought and downloaded to your computer from the internet or from CDs and then printed out. The advantage is that you can print out whichever sheet you wish. If you need to re-inforce a certain concept more you can usually print out that sheet again. Of course you will therefore need to have a computer and a printer.
Since 3rd grade math relies on the concepts that were learned during kindergarten, first and second grades, don't be afraid to start your child at a lower level.
A K-12 Digital education must provide creativity; customized learning based on the needs of the student, and cutting edge digital educational materials for grades kindergarten through 12th.