The purpose of this study was to synthesize, using meta-analytical methods, the research regarding phonemic awareness and phonics (decoding) instruction with students in grades 5 through 12 who read significantly below grade level expectations. Twenty-six studies published between 1975 and 2005 met the criteria for inclusion and analysis. A total of 1358 students participated in the studies (565 in control groups, 799 in treatment groups). The effect sizes of interventions = impact on achievement were calculated on five levels of dependent variables (word identification or word attack skills of sub-syllabic or single syllable levels, and decoding multi-syllabic words; oral reading fluency and accuracy of individual words or connected text; comprehending words or vocabulary; comprehending text; decoding, fluency and comprehension). Four separate analyses were presented: (a) the full data set; (b) the data set with outliers removed; (c) the full data set without one study (Mercer, Miller, Mercer, & Lane, 2000); and (d) the data without outliers and without the Mercer study. Although many of the studies exhibited medium to high effect sizes, none of the analyses at an alpha level of 0.05 reached statistical significance.

Because of the small number of studies and the variability of the population studied, the alpha level was relaxed to 0.25 to explore statistical significance of main effects or interaction effects at this level. The impact of group size and reading level on effect size was significant in many of the analyses at a 0.25 alpha level. The results were mixed for group size/intervention focus and reading level/intervention focus. Significant main effects were found for reading level (reading level*intervention focus) and the interaction between group size and intervention focus on word identification or word attack skills of sub-syllabic or single syllable levels, and decoding multi-syllabic words. The impact of reading level, group size, and intervention focus on effect size were not significant at any level. Limitations of this meta-analysis, features of interventions that show promise in accelerating the reading skills of delayed older readers, and suggestions for future research are also presented.