Purpose This study evaluated the efficacy of an explicit, combined metalinguistic training and grammar facilitation intervention aimed at improving regular past tense marking for nine children aged 5;10-6;8 (years;months) with developmental language disorder. Method This study used an ABA across-participant multiple-baseline single-case experimental design. Participants were seen one-on-one twice a week for 20- to 30-min sessions for 10 weeks and received explicit grammar intervention combining metalinguistic training using the SHAPE CODING system with grammar facilitation techniques (a systematic cueing hierarchy). In each session, 50 trials to produce the target form were completed, resulting in a total of 1,000 trials over 20 individual therapy sessions. Repeated measures of morphosyntax were collected using probes, including trained past tense verbs, untrained past tense verbs, third-person singular verbs as an extension probe, and possessive 's as a control probe. Probing contexts included expressive morphosyntax and grammaticality judgment. Outcome measures also included pre-poststandard measures of expressive and receptive grammar. Results Analyses of repeated measures demonstrated significant improvement in past tense production on trained verbs (eight of nine children) and untrained verbs (seven of nine children), indicating efficacy of the treatment. These gains were maintained for 5 weeks. The majority of children made significant improvement on standardized measures of expressive grammar (eight of nine children). Only five of nine children improved on grammaticality judgment or receptive measures. Conclusion Results continue to support the efficacy of explicit grammar interventions to improve past tense marking in early school-aged children. Future research should aim to evaluate the efficacy of similar interventions with group comparison studies and determine whether explicit grammar interventions can improve other aspects of grammatical difficulty for early school-aged children with developmental language disorder. Supplemental Material https://doi.org/10.23641/asha.11958771.