National Reading Panel Findings
Major points from the report of the National Reading Panel: Teaching Children to Read An Evidence-Based Assessment of the Scientific Research Literature on Reading and Its Implications for Reading Instruction, 2000
PA instruction helped all types of children improve their reading, including normally developing readers, children at risk for future reading problems, disabled readers, preschoolers, kindergartners, 1st graders, children in 2nd through 6th grades (most of whom were disabled readers), children across various SES levels, and children learning to read in English as well as other languages.
PA was found to help most children learn to spell, and its effect lasted well beyond the training. However, PA was not effective for improving spelling in disabled readers. This is consistent with other research indicating that disabled readers have a difficult time learning to spell.
PA instruction may be [sic] most effective when children are taught to manipulate with letters, when instruction is explicitly focused on one or two types of phoneme manipulations rather than multiple types, and when children are taught in small groups.