The purpose of this best-evidence synthesis was to identify promising interventions that align with a theoretical model of early writing development, targeting three components of early writing: transcription, text generation, and self-regulation. We determined the extent to which these interventions are "effective" for children who struggle with early writing skills, by calculating effect sizes for group and single subject designs, and examined the overall "quality" of the research. Twenty-five studies met inclusion criteria. Among group design studies, mean effects ranged from g = 0.19 to 1.17 for measures of writing quantity and from g = 0.17 to 0.85 for measures of writing quality. Percentage of all non-overlapping data (PAND) for single subject designs ranged from 83%-100% for measures of writing quantity. Interventions with the strongest evidence of effects "and" highest methodological quality are described in detail. Recommendations for research and practice are provided. [This paper was published in the "Journal of Learning Disabilities," Online First edition.]