Purpose: This study aims to investigate the learning potential of French-speaking children, either with typical development (TD) or with developmental language disorder (DLD), when learning an invented inflectional morphological rule. We tested the children's performance in learning pseudomorphemes of gender and number with dynamic assessment tasks.

Method: A total of 101 children with TD and 24 with DLD (M _age = 6;4 [years;months]) were recruited. The gender and number morphological tasks followed the same procedure, with (a) the introduction of a pseudoverb (PV) to describe the action of some animated characters, (b) the explicit teaching of the invented rule (i.e., the adding of a specific pseudomorpheme to the end of the PV), (c) the assessment of children's ability to apply the rule, and (d) the assessment of children's ability to generalize the rule to four other PV. Graduated prompts were provided to assist children in producing the six inflected forms for each PV.

Results: Effects of age and diagnosis were found for both tasks. Children with TD were able to learn and generalize the rule, demonstrating a mastery of the rule through to the last PV of the task. However, children with DLD needed more prompts to learn the rule and did not reach a plateau as their peers did. There was also an impact of nonverbal reasoning, but only in children with TD.

Conclusion: Our findings allow a better understanding of children's learning processes in inflectional morphology and provide clinicians with a new diagnostic tool, in line with the current definition of DLD.