One approach to help students with vocabulary acquisition is to increase their awareness of the morphological structure. A randomized control trial study published in Reading Research Quarterly examined the transfer effects of a morphological intervention for students with limited vocabulary knowledge in Danish, which is like English in that most words consist of more than one morpheme. Transfer effects are the essence that distinguishes morphological training from direct vocabulary training.
About 12 students with the most limited Danish vocabulary knowledge from each of 29 fifth-grade classes in 13 schools participated in the trial (N=332). The students within each class were randomly assigned to a control group or to one of two treatment groups: a morphological vocabulary intervention or a context-based vocabulary intervention. Students in the two treatment groups received 24 lessons of 30 minutes separately, two days per week. The interventions were delivered by 5 trained speech-language therapists, each responsible for instruction in both intervention groups in two or three schools.
The results showed that:
- In the short-term, the morphological intervention had statistically significant positive effect sizes for morphological segmentation, word knowledge, and reading comprehension with taught words (+0.24).
- But the intervention had no significant effects on standardized measures of vocabulary or reading comprehension.
- Ten months after the intervention, the follow-up posttest results showed that the intervention had long-term significant effects on students’ abilities to segment and explain taught words and transfer words.
The outcomes implied that a morphological intervention could increase students’ ability to understand unfamiliar words with trained morphemes and morphologically complex words with untrained but common roots.