My 11-year-old niece may have to repeat the fifth grade -- she took a readiness test for sixth grade and she failed. She has to attend summer school, but what can we do at home to help her?
The best way to address your niece's readiness is to give her consistent individual help. Work out a schedule for the adults in her life to help her work on the skills with which she is having trouble. Often children respond better to people other than their parents, so you may be able to find a high-school student in the neighborhood who would be willing to help tutor your niece, either for free or for a nominal amount.
Look in a teacher-supply store for workbooks at your niece's level. Talk with her teacher and the technology specialist at her school to find recommended software titles that she could use on the computer.
Whatever you decide to do, have your niece work on improving her skills daily throughout the summer. Pursuing this in a hit-or-miss fashion will only frustrate all of you and will not help her learn the material.