Enhancing the Intensity of Vocabulary Instruction for Preschoolers at Risk: The Effects of Group Size on Word Knowledge and Conceptual Development

An indicator of the effect of the intervention, the improvement index can be interpreted as the expected change in percentile rank for an average comparison group student if that student had received the intervention.

For more, please see the WWC Glossary entry for improvement index.

An outcome is the knowledge, skills, and attitudes that are attained as a result of an activity. An outcome measures is an instrument, device, or method that provides data on the outcome.

A finding that is included in the effectiveness rating. Excluded findings may include subgroups and subscales.

The sample on which the analysis was conducted.

The group to which the intervention group is compared, which may include a different intervention, business as usual, or no services.

The timing of the post-intervention outcome measure.

The number of students included in the analysis.

The mean score of students in the intervention group.

The mean score of students in the comparison group.

The WWC considers a finding to be statistically significant if the likelihood that the finding is due to chance alone, rather than a real difference, is less than five percent.

The WWC reviews studies for WWC products, Department of Education grant competitions, and IES performance measures.

The name and version of the document used to guide the review of the study.

The version of the WWC design standards used to guide the review of the study.

The result of the WWC assessment of the study. The rating is based on the strength of evidence of the effectiveness of the intervention. Studies are given a rating of Meets WWC Design Standards without Reservations, Meets WWC Design Standards with Reservations, or >Does Not Meet WWC Design Standards.

A related publication that was reviewed alongside the main study of interest.

Study findings for this report.

Based on the direction, magnitude, and statistical significance of the findings within a domain, the WWC characterizes the findings from a study as one of the following: statistically significant positive effects, substantively important positive effects, indeterminate effects, substantively important negative effects, and statistically significant negative effects. For more, please see the WWC Handbook.

The WWC may review studies for multiple purposes, including different reports and re-reviews using updated standards. Each WWC review of this study is listed in the dropdown. Details on any review may be accessed by making a selection from the drop down list.

Tier 1 Strong indicates strong evidence of effectiveness,
Tier 2 Moderate indicates moderate evidence of effectiveness, and
Tier 3 Promising indicates promising evidence of effectiveness, as defined in the non-regulatory guidance for ESSA and the regulations for ED discretionary grants (EDGAR Part 77).