| Domain of impairment | Classmates | Extremely preterm children | ||
| All, n (%) | Boys, n (%) | Girls, n (%) | All, n (%) | |
| General cognitive ability | (n = 153) | (n = 101) | (n = 118) | (n = 219) |
| No impairment | 129 (84.3) | 23 (22.8) | 46 (39.0) | 69 (31.5) |
| Mild impairment | 22 (14.4) | 28 (27.7) | 35 (29.7) | 63 (28.8) |
| Moderate impairment | 2 (1.3) | 27 (26.7) | 28 (23.7) | 55 (25.1) |
| Severe impairment | 0 (0.0) | 23 (22.8) | 9 (7.6) | 32 (14.6) |
| Reading | (n = 153) | (n = 97) | (n = 115) | (n = 212) |
| No impairment | 136 (88.9) | 40 (41.2) | 62 (53.9) | 102 (48.1) |
| Mild impairment | 14 (9.2) | 22 (22.7) | 24 (20.9) | 46 (21.7) |
| Moderate impairment | 3 (2.0) | 10 (10.3) | 13 (11.3) | 23 (10.8) |
| Severe impairment | 0 (0.0) | 25 (25.8) | 16 (13.9) | 41 (19.3) |
| Maths | (n = 153) | (n = 99) | (n = 116) | (n = 215) |
| No impairment | 132 (86.3) | 29 (29.3) | 36 (31.0) | 65 (30.2) |
| Mild impairment | 19 (12.4) | 23 (23.2) | 33 (28.4) | 56 (26.0) |
| Moderate impairment | 2 (1.3) | 15 (15.2) | 27 (23.3) | 42 (19.5) |
| Severe impairment | 0 (0) | 32 (32.3) | 20 (17.2) | 52 (24.2) |
Impairment is classified relative to the mean (SD) of classmates on each scale. No impairment: scores >−1 SD; mild impairment: scores <−1 to −2 SD; moderate impairment: scores <−2 to −3 SD; severe impairment: scores <−3 SD.