The current best evidence meta-analysis reanalyzed the data from a meta-analysis by Graham et al. (J Educ Psychol 115:1004-1027, 2023). This meta-analysis and the prior one examined if teaching writing improved the writing of students in Grades 6 to 12, examining effects from writing intervention studies employing experimental and quasi-experimental designs (with pretests). In contrast to the prior meta-analysis, we eliminated all N of 1 treatment/control comparisons, studies with an attrition rate over 20%, studies that did not control for teacher effects, and studies that did not contain at least one reliable writing measure (0.70 or greater). Any writing outcome that was not reliable was also eliminated. Across 148 independent treatment/control comparisons, yielding 1,076 writing effect sizes (ESs) involving 22,838 students, teaching writing resulted in a positive and statistically detectable impact on students' writing (ES = 0.38). Further, six of the 10 writing treatments tested in four or more independent comparisons improved students' performance. This included the process approach to writing (0.75), strategy instruction (0.59), transcription instruction (0.54), feedback (0.30), pre-writing activities (0.32), and peer assistance (0.59). In addition, the Self-Regulated Strategy Development model for teaching writing strategies yielded a statistically significant ES of 0.84, whereas other approaches to teaching writing strategies resulted in a statistically significant ES of 0.51. The findings from this meta-analysis and the Graham et al. (2023) review which included studies that were methodologically weaker were compared. Implications for practice, research, and theory are presented.