|The current practice for treating speech sound disorders includes initiating treatment only after the expected age of acquisition has passed, according to developmental normative data. Unfortunately, for children who experience late-acquired sound errors, this practice misses a period of accelerated learning that occurs between the ages of 4-6 (Shriberg, Gruber, & Kwiatkowski, 1994). Instead, this practice causes therapists to initiate treatment for late-acquired sounds during a plateau of learning that occurs between the ages of 6-7 to over 8.5 years (Shriberg et al., 1994). Generally speaking, early intervention is thought to be the most effective in the treatment of developmental communication disorders. Therefore, the present study investigated whether the age of treatment contributed to the efficacy and efficiency of articulation therapy for late-acquired sounds, such as /ɹ/ or / θ /. A repeated, multiple baselines, single-subjects study investigated two age groups who misarticulated late-acquired sounds: a younger group (4-5) and an older group (7-8). These age groups capture each side of the developmental trajectory of speech sound development identified by Shriberg et al. (1994). Each child received a criterion-based, standardized two-phase articulation therapy protocol, and pre- and posttest measurements were taken using speech probes, standardized articulation tests, and acoustic analysis. These measurements allowed for an examination of treatment efficacy through the measurement of both subjective accuracy and objective accuracy as compared with the ages of the children. In addition, treatment efficiency was measured by calculating the number and duration of sessions for each phase, and overall. The results of this study indicated that younger children achieved a level of accuracy similar to that of older children as a result of treatment for late-acquired sounds, and younger children’s slope of treatment accuracy over time was steeper than that of older children, suggesting that younger children were more accurate sooner than older children. For young children, a higher degree of naturalness was observed than for old children, as measured by acoustic analysis. These findings serve as an initial probe to challenge the current method of speech therapy practice for late-acquired sounds.