ns = not statistically significant

¹ The standard deviation across all students in each group shows how dispersed the participants' outcomes are: a smaller standard deviation on a given measure would indicate that participants had more similar outcomes. The student-level standard deviations were requested by the WWC and submitted by the study authors. Thus, the standard deviations reported here are different from the standard deviations in the study report.
² This review focuses on variations among students both in their perceptions of their own behavior and their perceptions of the behavior of their peers. Additional teacher-reported outcomes were excluded because the effects on students (effect size) could not be estimated for this outcome. The teacher survey represented global ratings at the classroom level rather than ratings of individual students. And standard deviations for this measure represented variations among teachers rather than variations among students.
³ The Connect with Kids mean equals the comparison group mean (column 2) plus the mean difference (difference between treatment and comparison gain scores; column 3). The mean difference reported here takes into account students' change from baseline (gain scores), which were used to calculate effect size. So, the intervention mean reported here is different from the mean in the study report. For an explanation of effect size calculation, please see the Technical Details of WWC-Conducted Computations.
⁴ Although Connect with Kids is intended for schoolwide implementation, this study tested it using individual classrooms. Consequently, results may not reflect the true nature of the program, when enacted school-wide and involving all teachers and students. Positive differences and effect sizes favor the intervention group; negative differences and effect sizes favor the comparison group.
⁵ Statistical significance is the probability that the difference between groups is a result of chance rather than a real difference between groups. The level of statistical significance was calculated by the WWC and where necessary, corrects for clustering within classrooms or schools, and for multiple comparisons. For an explanation, see the WWC Tutorial on Mismatch. See the Technical Details of WWC-Conducted Computations for the formulas the WWC used to calculate the statistical significance. In the case of theConnect with Kids report, a correction for multiple comparisons, but not for clustering, was needed.
⁶ The improvement index represents the difference between the percentile rank of the average student in the intervention condition and the average student in the comparison condition. The improvement index can take on values between -50 and +50, with positive numbers denoting favorable results.
⁷ The study also reported on an additional statistical analysis that controlled for percentage of female and minority students. This analysis found a statistically significant positive effect on total scores on the elementary school student survey parts 1 and 2. But, because of incomplete data, the WWC could not confirm the statistical significance of these findings. The reviewed statistical analyses of elementary and middle/high school students' outcomes did not take into account demographic characteristics of the sample.
⁸ This row provides the study average, which is also the domain average in this case. The WWC-computed domain average effect size is a simple average rounded to two decimal places. The domain improvement index is calculated from the average effect size.

¹ For rating purposes, the WWC considers the statistical significance of individual outcomes and the domain level effect. The WWC also considers the size of the domain level effect for ratings of potentially positive effects. See the WWC Intervention Rating Scheme for a complete description.