Dear Ashley,
Keeping your grades from your mom probably won't work since she's likely to find out anyway. Then she'll be doubly angry, not just about the failed test, but also because you purposely kept the information from her. Instead try the following: think about what you should do differently in the future to make it less likely that you'll fail a test—make a schedule for studying and keep to it, watch less television, and take notes to help you remember facts. Then when you tell your mom about the failed test, you can also tell her that you have a plan to help you get better grades in the future. Hopefully, she'll recognize that you're trying to do something positive and will not ground you.