| Code | Definition |
|---|---|
| a | Preschool (up to, but not including, kindergarten) |
| b | Primary (kindergarten through grade 3 |
| c | Preadolescent (grades 4 through 8) |
| d | Adolescent (grades 9 through 12) |
| g | General (any audience level) |
| j | Juvenile (all through age fifteen or grade 9) |