O’Brien Press books are colour-coded with reading age flags. This guide indicates which flags are most appropriate for different class levels, to support you in choosing the right book for your students.
| Reading age flag | Republic of Ireland | Northern Ireland | |
 | Black flag Picture books | Usable throughout the school (but especially Junior Infants, Senior Infants) | Usable throughout the school (but especially Year 1 [P1]) |
 | Purple flag Reading level 5+ | Senior Infants, First Class (also Second Class) | Year 2 [P2]. Key Stage 1 |
 | Yellow flag Reading level 6+ | Second Class (also First Class, Third Class) | Year 3 [P3]. Key Stage 1 |
 | Red flag Reading level 8+ | Third Class, Fourth Class | Year 4, Year 5 [P4, P5]. Key Stages 1 & 2 |
 | Blue flag Reading level 10+ | Fifth Class, Sixth Class | Year 6, Year 7 [P6, P7]. Key Stage 2 |
 | Green Flag Reading level 12+ | First Year, Second Year (second-level schools) | Year 8, Year 9, Year 10 (secondary schools). Key Stage 3 |
