A research design in which participants are measured on the dependent variable before (pre-test) and after (post-test) a treatment or intervention. The difference between pre-test and post-test scores provides evidence of change. This is the default measurement structure in SLA intervention research, underpinning both true experimental and quasi-experimental studies.
A single group is tested before and after treatment. No comparison group. This is the weakest design: any improvement could be due to maturation, testing effects, history, or regression to the mean rather than the treatment itself.
A treatment group and a control/comparison group, both pre- and post-tested. The standard quasi-experimental arrangement. Comparing group gains controls for maturation and history (assuming both groups experience them equally).
Developed by Solomon (1949). Four groups:
| Group | Pre-test | Treatment | Post-test |
|---|---|---|---|
| 1 | Yes | Yes | Yes |
| 2 | Yes | No | Yes |
| 3 | No | Yes | Yes |
| 4 | No | No | Yes |
The design controls for pre-test sensitisation, the possibility that taking the pre-test itself changes how participants respond to the treatment or post-test. If Groups 1 and 3 show different post-test results, the pre-test interacted with the treatment. Powerful but resource-intensive, it requires four times the sample of a one-group design. Rarely used in SLA research due to the large participant numbers required.
A single post-test immediately after treatment shows whether learning occurred but not whether it endured. Delayed post-tests (administered days, weeks, or months later) assess durability. This matters especially for distinguishing genuine acquisition from short-term performance gains.
Norris & Ortega (2000) found that studies with delayed post-tests showed smaller effect sizes than those with immediate post-tests only, suggesting some reported gains reflect temporary rather than lasting learning.
Simple difference: post-test minus pre-test. Intuitive but statistically problematic because gain scores are unreliable and correlate with pre-test scores (students who start lower have more room to improve).
Uses pre-test scores as a covariate to statistically adjust for initial group differences. Preferred over gain scores because it controls for regression to the mean and handles non-equivalent groups more effectively. The standard recommendation for quasi-experimental classroom studies.
Treats time (pre, post, delayed post) as a within-subjects factor. Appropriate when the same participants provide data at multiple time points.