Word learning in children with developmental language disorder: A meta-analysis testing the encoding hypothesis

Many children with Developmental Language Disorder (DLD) find learning new words difficult, which negatively affects their educational and psycho-social outcomes. Word learning involves encoding, consolidation and reconsolidation of words, but the most challenging phase and factors which moderate word learning remain unclear.

We conducted a systematic review and meta-analysis to determine which phase is most challenging and which factors predict oral word learning success in children with DLD. The search including PsycINFO, PubMed, Web of Science, and LLBA identified forty-six studies published before April 2024 comparing children with DLD and typically developing (TD) age-matched peers in word learning tasks. Seventy-eight effect sizes were calculated for encoding (n DLD = 1462, n TD = 2161), eight for consolidation (n DLD = 107, n TD = 112), and 19 for reconsolidation (n DLD = 296, n TD = 278).

The random effect model identified an effect for encoding (k = 78, d = 0.82, [0.66, 0.98], p < .001) but not consolidation (k = 8, d = −0.2, [−0.68, 0.29], p = .43) or reconsolidation (k = 19, d = 0.23, [−0.14, 0.59], p = .22) of new words. The moderator analysis via random effects models identified verbal short-term memory and lexical knowledge as significant moderators of encoding, while word length was the most important task characteristic.

Despite limited data for consolidation and reconsolidation, our findings provide new insights into oral word learning difficulties in children with DLD. These insights help clinicians and teachers identify support strategies while also highlighting gaps in existing research, driving future studies forward.