Expressive language outcomes measured by MLU and the Index of
Productive Syntax (IPSyn) at ages 3;0 and 4;0 were investigated in 34
late talkers with normal receptive language identified between 2;0 to 2;7
and 16 typically developing comparison children matched on age, SES,
and nonverbal ability. Late talkers made greater gains than comparison
children between 3;0 and 4;0 in both MLU and IPSyn raw score.
However, when age-standardized z-scores were analysed, the late talkers
were about 2·5 standard deviations below comparison children on both
measures at both ages. At 3;0, 41% of the late talkers had MLUs above
the 10th percentile based on Scarborough's (1990) benchmark sample;
by 4;0, 71% did so. Using the IPSyn, a more stringent measure, 34%
scored above the 10th percentile at 3;0 and only 29% did so at 4;0.
MLU was significantly correlated with the IPSyn at both ages for the
late talkers, but only at 3;0 for the comparison children. A converging
set of regression analyses indicated no group differences in the predictive
relationship between MLU and IPSyn, suggesting that the late talkers
were delayed on both measures but not deviant in their development.