Make dinner a meal during which you can find out what your child learned in school that day. With younger children, you can "play dumb" and have them explain their lessons to you by pretending you don't understand them. The recitation will help to implant the lessons in their mind. You will also be able to backtrack to that lesson days later to reinforce it.
Turn the television off for awhile each evening for family reading time. This can include anything from newspapers and magazines to a library book. Have younger children read aloud to you then chat about what they just read to facilitate comprehension. Ask older children to tell you about what they're reading and ask for their impressions of it.
Basic math skills are part of everyday life. Use each opportunity when it presents itself. Let your child count your change from a purchase and make sure it is right. Ask her to help you prepare meals by measuring ingredients, or to calculate time and distance when you drive somewhere. Turn the daily projects into a game with a reward system to make it fun for younger students.
Make sure your child gets adequate sleep the night before the test so he's not fatigued and working at a disadvantage. A healthy breakfast is important as well. Ask his teacher if you can send fruit juice or sports drink to school with him while testing. Don't put additional pressure on your child by stressing how important the test is. If you've been working with him on a regular basis, the knowledge he'll need will be firmly in place.
Last-minute cramming and drills will probably not help your child and may only stress her out. Monitor her progress with her teacher on a regular basis to pin down any areas where she may need help well in advance of the test so you can work with her on them. If your child is having difficulty in a certain area, her school can offer remedial help. There are special tests and procedures available for students with learning disabilities.