Evaluation of an Explicit Approach

This study is a randomized trial with two phases. Phase 1 is a traditional randomized trial during which eligible and consenting participants will be randomized equally to one of two interventions: Explicit-added or Implicit-only. Randomization is blocked by age (5- & 6-year-olds; and 7- to 9-year-olds) and receptive language ability to ensure that ages are matched across groups and that half of the participants in each treatment group have receptive language skills below average. A standard score of 80 is used to categorize participants (below average: < 80; average: ≥ 80) based on the Receptive Language Index of the Clinical Evaluation of Language Fundamentals (CELF). Participants are also stratified based on child gender. All participants will complete 32 sessions (8 sessions per target in blocks of 4). In Phase 2, participants in both the Explicit-added and Implicit-only groups will be re-randomized based on level of mastery on treatment goals. Participants who are considered treatment "Masters" and have achieved the criterion of 80% accuracy on all target forms will be re-randomized to receive no further treatment or a round of the alternative treatment. Participants who have not yet mastered each of the four target forms (< 80% accuracy) will be re-randomized to receive another round of either the same treatment or the alternative treatment.

Study participants will include 155 children with language impairment, aged 5 through 9 years, accounting for a 10% attrition rate resulting in 140 participants. This age includes children who likely experience difficulties with the grammatical forms targeted in intervention and who are receiving intervention for weaknesses in grammatical language. Researchers will recruit participants with an effort to maximize participant diversity based on ethnicity and parental education. We aim to recruit a representative sample of children with DLD, which will include more boys than girls. Participants will not have any indication of other significant conditions to which their impairment may be attributed, such as autism spectrum disorder, Down syndrome, seizure disorder, or hearing impairment. Participants with a diagnosis of attention deficit/hyperactivity disorder will be included due to high rate of co-morbidity.

Inclusion criteria

Study participants will include children with language impairment, aged 5 through 9 years. Participants will not have any indication of other significant conditions to which their impairment may be attributed, such as autism spectrum disorder, Down syndrome, seizure disorder, or hearing impairment. Participants with a diagnosis of attention deficit/hyperactivity disorder will be included due to high rate of co-morbidity (see Redmond, 2016). Additionally, participants will meet the following criteria:

• No evidence of significant cognitive delay;
• Evidence of language impairment;
• Evidence of deficits on expressive grammatical forms: score below 30% accuracy on at least two of the following forms: third person singular -s, regular past tense -ed, auxiliary is/are in statements, auxiliary do/does in questions;
• Typical hearing and vision, with correction if necessary;
• Native English speaker with English spoken in the home by at least one primary caregiver since birth;
• Speaker of Mainstream American English;
• Be able to articulate final-position phonemes /s/, /z/, /t/, and /d/; and
• Majority of utterances (> 50%) include subject and verb in obligated contexts based on a 20-min conversational language sample to ensure appropriateness of study intervention.

Exclusion criteria

Participants will be excluded if there is no indication of language impairment, and they are not aged 5 through 9 years. Participants will also be excluded if there is indication of other significant conditions to which their impairment may be attributed, such as autism spectrum disorder, Down syndrome, seizure disorder, or hearing impairment. Additionally, participants will be excluded in they meet the following criteria:

• Evidence of significant cognitive delay;
• No evidence of deficits on expressive grammatical forms: score below 30% accuracy on at least two of the following forms: third person singular -s, regular past tense -ed, auxiliary is/are in statements, auxiliary do/does in questions;
• Atypical hearing and vision, with correction if necessary;
• Non-native English speaker;
• Speaker of Non-mainstream American English;
• Unable to articulate final-position phonemes /s/, /z/, /t/, and /d/; and
• Non-majority of utterances (< 50%) include subject and verb in obligated contexts based on a 20-min conversational language sample to ensure appropriateness of study intervention.