This paper reviews research on outcomes of writing programmes for students in Years 3 to 13 in England, or grades 2 to 12 in the US. Studies had to meet rigorous standards of research including use of randomised or well-matched control groups, measures independent of the programme developers, researchers, and teachers, and adequate sample size and duration. Fourteen studies of 12 programmes met the standards. Twelve (86%) were randomised, two matched. Programmes were divided into three categories. Student achievement effects on writing were positive on average in all categories (Effect Size=+0.18), with similar outcomes for writing programmes focused on the writing process (ES=+0.17), those using cooperative learning (ES=+0.16) and those focusing on interactions between reading and writing (ES=+0.19). [For the related guidance report, see ED612217.]