TABLE 4. Levels of performance in reference population.

Age bands	Descriptive Mean (SD)	Superior performance >+3 SD	Accelerated performance +3 to +2 SD	Normal range +2 to −2 SD	Moderate delay −2 to −3 SD	Severe delay <−3 SD
6–8	15.86 (2.97)	25	22	21–11	10	7
9–11	20.44 (2.50)	28	26	25–16	18	12
12–14	27.35 (4.56)	41	33	39–21	19	14
15–17	34.29 (5.64)	51	40	39–23	22	17
18–20	40.29 (3.09)	50	46	45–35	34	31
21–23	43.63 (2.68)	51	49	48–39	38	35
24–26	44.85 (3.84)	56	51	50–39	38	33
27–29	48.28 (4.95)	63	54	52–41	40	33
30–32	50.75 (4.95)	66	56	55–41	40	36
33–35	53.06 (4.55)	67	59	58–44	43	39