A true experiment is the gold standard for establishing causal relationships. It requires three elements: (1) random assignment of participants to conditions, (2) manipulation of an independent variable (the treatment), and (3) a control or comparison group. When these conditions hold, differences on the dependent variable can be attributed to the treatment rather than to pre-existing group differences.
| Feature | Requirement |
|---|---|
| Random assignment | Participants allocated to groups by chance |
| Treatment manipulation | Researcher controls the independent variable |
| Control group | At least one group receives no treatment or a placebo |
| Pre/post measurement | Outcome measured before and after intervention |
Random assignment is the critical distinction from Quasi-Experimental Design. It distributes confounding variables (motivation, aptitude, proficiency) roughly equally across groups, strengthening Internal Validity.
True experiments are rare in classroom SLA research for practical and ethical reasons:
As a result, the vast majority of classroom intervention studies use quasi-experimental designs with intact groups, and true RCTs remain largely confined to laboratory settings or large-scale educational trials.
Strengths: highest Internal Validity; permits causal inference; results are interpretable via standard statistical tests; Effect Size comparisons are straightforward.
Limitations: low Ecological Validity when conducted in labs; difficult to implement in educational contexts; Hawthorne Effect may confound results; randomisation does not guarantee equivalence in small samples (common in SLA).