Found effects

The WWC found Ladders to Literacy to have potentially positive effects on alphabetics and fluency and mixed effects on comprehension

Improvement index

The WWC computes an improvement index for each individual finding. In addition, within each outcome domain, the WWC computes an average improvement index for each study and an average improvement index across studies (see Technical Details of WWC-Conducted Computations). The improvement index represents the difference between the percentile rank of the average student in the intervention condition versus the percentile rank of the average student in the comparison condition. Unlike the rating of effectiveness, the improvement index is based entirely on the size of the effect, regardless of the statistical significance of the effect, the study design, or the analyses. The improvement index can take on values between -50 and +50, with positive numbers denoting results favorable to the intervention group.

The average improvement index for alphabetics is +25 percentile points across three studies, with a range of +8 to +47 percentile points across findings. One additional study that showed positive effects in alphabetics was not included in this average and range because the student-level improvement index could not be computed by the WWC.

The improvement index for fluency is +26 percentile points for the single finding in one study.

The average improvement index for comprehension is +9 percentile points across the three studies, with a range of +1 to +17 percentile points across findings.

Summary

The WWC reviewed six studies on Ladders to Literacy. ¹⁴ Four of these studies met WWC standards with reservations; the others did not meet WWC evidence screens. Based on these studies, the WWC found potentially positive effects on alphabetics and fluency and mixed effects on comprehension. The evidence presented in this report may change as new research emerges.