Morphemes matter: A small scale randomised control trial of vocabulary intervention focusing on affixes for adolescents with (developmental) language disorder

To investigate whether morphological intervention improves understanding of affixes in adolescents with a language disorder and whether progress generalises. A total of 25 adolescents aged 13–15 years participated in this single-blind trial with random allocation. All participants had a language disorder; 18 with developmental language disorder, four with associated genetic conditions, and three with autism. A total of 11 participants received twice-weekly morphological intervention for 30 min with a speech-language pathologist for 8 weeks, while 14 received intervention as usual. Two tests were administered pre- and post-intervention: Affix definition and an adapted rehit task, which tested participants’ ability to work out the meaning of novel words containing affixes. To investigate generalisation to untaught affixes, only half of the affixes were taught in intervention. Those in the intervention group made significantly more progress than controls on both tasks, but only on taught affixes. Therefore, learning generalised to understanding the meaning of taught affixes in combinations with new roots (adapted rehit task) but did not generalise to untaught affixes on either task. The intervention was effective and learning generalised to other words containing taught affixes. Intervention for affixes has potential to greatly increase understanding of vocabulary following relatively small amounts of intervention.