The analysis reviewed 71 studies of reading interventions, each of
which had an intervention and control group, post-tests, and follow-up
data an average of 11 months later. Among the findings were that normal
readers appeared to profit least from reading interventions,
particularly at follow-up.
Improvement was not sustained for interventions in preschool: effect
sizes fell from +0.34 to +0.12 at follow-up. By contrast, in Years 2 and
3, the effect size only diminished from +0.40 to + 0.26, and for Years 4
and 5, the effect size increased from +0.35 to + 0.43 at follow-up.
The greatest effect sizes at follow-up appeared to result from interventions with a comprehension component.
Source: A Meta-Analysis of the Long-Term Effects of
Phonemic Awareness, Phonics, Fluency, and Reading Comprehension
Interventions (2016), Journal of Learning Disabilities.