Related Experiment Video
Updated: Feb 9, 2026

Validation of a Psychosocial Intervention on Body Image in Older People: An Experimental Design
Published on: May 31, 2021
Effectiveness of a small-group vocabulary intervention programme: evidence from a regression discontinuity design
Hannah Dyson1, Jonathan Solity2, Wendy Best1
1Division of Psychology and Language Sciences, University College London (UCL), London, UK.
Background:
Children's vocabulary knowledge is closely related to other measures of language development and to literacy skills and educational attainment.
Aim:
To use a regression discontinuity design (RDD) to evaluate the effectiveness of a small-group vocabulary intervention programme for children with poor vocabulary knowledge.
Methods & Procedures:
The vocabulary knowledge of children (N = 199) aged 6-9 years was assessed in six classes. Based on scores at the initial assessment, children with low vocabulary scores for their age were assigned to an intervention group (43 children), with the remaining 156 children assigned to a control group. Children in the intervention group received two to three small-group weekly teaching sessions over a 10-week period. All children were retested post-intervention on the same measures of vocabulary knowledge.
Outcomes & Results:
The intervention group showed significant improvements in their knowledge of the meanings of the taught words at post-test (an additional 3.95 words learned [95% confidence interval (CI) = 2.70-5.20] compared with the control group; d = 1.20), but the effects did not generalize to untaught words.
Conclusions & Implications:
A small-group vocabulary intervention programme is effective for teaching word meanings to 6-9-year-old children with poor vocabulary skills. This study provides further evidence that the RDD is an effective method for evaluating educational interventions.
Related Concept Videos
Regression Toward the Mean
The Evidence for Evolution
Multiple Regression
Farmers can use multiple regression to determine the crop yield based on more than one factor, such as water availability, fertilizer, soil properties, etc. Here, the crop yield is the response or dependent variable as it depends on the other independent variables. The analysis requires the construction of a scatter plot...
Limits with Oscillating Discontinuities
Improper Integrals: Discontinuous Integrands
Correlation and Regression

