The Preliminary SAT -- also known as the National Merit Scholarship Qualifying Test -- is a standardized test administered in the fall of each year. Students in 11th grade take the PSAT/NMSQT to qualify for scholarships; younger students can take it as well to test their abilities. PSAT grading corresponds closely with that of the SAT, and a score in the top percentiles can make you eligible for certain scholarships.

PSAT Sections and Selection Index

The PSAT is split into three sections: Critical Reading, Mathematics and Writing Skills. Each section is graded in a range from 20 to 80 points; the best PSAT score possible is thus an 80 in each section. In addition, the three scores are combined to determine a student's selection index. If you have scores of 50 in Critical Reading, 67 in Mathematics and 59 in Writing Skills, your selection index is 176. The average selection index for 11th-graders taking the PSAT is around 140.

Percentiles and Scholarship Qualifications

The selection index is used to determine the percentage of students you have scored higher than in that year. This is referred to as your percentile. For instance, in 2010, students with selection indexes of over 200 were in the top 3 percent of those taking the test, or the 97th percentile. Students in the top percent -- the 99th percentile -- had selection indexes over 210.

The selection index is used by the National Merit Scholarship Corporation to determine the minimum requirements for scholarship eligibility. While the qualifying selection index can change each year and also varies by geographic region, you generally need an index of least 201 to qualify as a National Merit Semifinalist, roughly in the top 3 percent of 11th-graders.