Additional repetition and practice of skills my daughter learns at school really helps to cement them. Flash Kids workbooks are fun for her, and show me she has learned whatever we're working on.
If you have a grade school aged kid, you can probably relate. I don't have the energy to create additional exercises for her, after the minimal amount of homework she has is done. I can page through a workbook and find additional material. During breaks, like over the summer, I can ask her to do a few pages whenever we appear to have too much time on our hands.
The Flash Kids series has become very popular in our home. We started with the Math Skills workbook, and having seen how well it worked for us we got the Complete Curriculum edition. Each exercise has easy to grok instructions, colorful pages and just the right amount of work to encourage, but not overwhelm, the kid. Some of the mysterious new-new-new math we're doing is also made clear by the Flash Kids illustrations and instructions, filling in gaps for me.
If you are looking for some grade appropriate workbooks for your elementary schooler, I like these.
Complete Curriculum: Grade 3 (Flash Kids Harcourt Family Learning) via Amazon