23.⁴ The scores are grouped into five categories based on the percentile score ranges shown in Table 2-A-1. Persons who score in Categories I and II tend to be above average in trainability; those in Category III, average; those in Category IV, below average; and those in Category V, markedly below average. By law, Category V applicants and those in Category IV who have not graduated from high school are not eligible for enlistment. Over and above these legal restrictions, each Service prescribes its own aptitude and education criteria for eligibility. Each Service uses combinations of ASVAB test scores to determine an applicant’s aptitude and eligibility for different military occupations.

DoD implemented a three-tier classification of education credentials in 1987, as follows:

• Tier 1—Regular high school graduates, adult diploma holders, and nongraduates with at least 15 hours of college credit.

• Tier 2—Alternative credential holders, including those with a General Education Development (GED) certificate of high school equivalency.

• Tier 3—Those with no education credential.

The system was developed after research indicated a strong relationship between education credentials and successful completion of the first