Find out what the student's weaknesses are. If one of your students struggles with reading comprehension and does not do well with the reading section of a test, discuss your concerns with the student and offer to give him extra assistance with this subject after school, during the lunch break or before school starts.
Give your student extra assignments in addition to the regular homework. If you're teaching social studies and one of your student has not done well on this portion of the standardized test, give her some age-appropriate history books, in addition to the social studies textbook, so she can read more about aspects of social studies such as geography and American history. Also create some study questions based on the nonfiction books for her to answer so she can practice for the test.
Hold a meeting with the student's parents. During the meeting, discuss the portions of the standardized test that your student struggles with and then mention the ways in which you've been helping him or her improve so far. Also answer any questions the parents may have and suggest practical methods they can use to help the student do better on the test.