Or, if it measures the ability to learn, it can affect a child's placement in school. So it's important to do well on tests. Besides, the ability to do well on tests can help throughout life in such things as getting a driver's license, trying out for sports, or getting a job. Without this ability, a person can be severely handicapped. Your child can develop this ability, and you can help the child do it.
Tests are yardsticks.
Schools use them to measure, and then improve education. Some tell schools that they need to strengthen courses or change teaching techniques. Other tests compare students by schools, school districts, or cities. And that's very important. They will play a role in determining grades.