While there are many ways to author text today, writing with paper and pen (or pencil) is still quite common at home and work, and predominates writing at school. Because handwriting can bias readers' judgments about the ideas in a text and impact other writing processes, like planning and text generation, it is important to ensure students develop legible and fluent handwriting. This meta-analysis examined true- and quasi-experimental intervention studies conducted with K-12 students to determine if teaching handwriting enhanced legibility and fluency and resulted in better writing performance. When compared to no instruction or non-handwriting instructional conditions, teaching handwriting resulted in statistically greater legibility (ES = 0.59) and fluency (ES = 0.63). Motor instruction did not produce better handwriting skills (ES = 0.10 for legibility and -0.07 for fluency), but individualizing handwriting instruction (ES = 0.69) and teaching handwriting via technology (ES = 0.85) resulted in statistically significant improvements in legibility. Finally, handwriting instruction produced statistically significant gains in the quality (ES = 0.84), length (ES = 1.33), and fluency of students' writing (ES = 0.48). The findings from this meta-analysis provide support for one of the assumptions underlying the Simple View of Writing (Berninger et al., "Journal of Educational Psychology," 94, 291-304, 2002): text transcription skills are an important ingredient in writing and writing development.