A literature search of articles written between 1980 and 2011 was carried out to find studies that met the following criteria:
- The studies compared children taught in classes using a given science programme or practice with those in control classes using an alternative programme or standard methods.
- The programme or practice had to be one that could, in principle, be used in ordinary science classes (ie, it did not depend on conditions unique to the experiment).
- Random assignment or matching with appropriate adjustments for any pretest differences (eg, analyses of covariance) had to be used. Studies without control groups, such as pre-post comparisons and comparisons to “expected” scores, were excluded.
- Pretest data had to be provided, unless studies used random assignment of at least 30 units (individuals, classes, or schools) and there were no indications of initial inequality.
- The dependent measures included quantitative measures of science performance that were not excessively aligned with the experimental (but not control) treatment.
- A minimum study duration of 4 weeks was required (see full report for rationale).
- Studies had to have at least two teachers and 15 pupils in each treatment group.