It is “Know Thy Impact.” When teachers walk into a classroom (or principal into a staffroom) and ask about knowing their impact then all good things follow for the students. This begs questions about what is meant by impact, for whom and how many derive the benefits of this impact, and the magnitude or level of gain relating to this impact.

### Articles in this section

- Why does the Visible Learning research use effect sizes?
- Why do you use an effect size of d=0.40 as a cut-off point and basically ignore effect sizes lower than 0.40?
- What is the preferred timescale over which an effect size can be calculated?
- Is there a bias when using effect sizes in favor of lower achieving students?
- What caution should I take when calculating an effect size?
- Why are effect sizes used when conducting meta-analysis?
- Why can an effect size of 0.40 be gained in a shorter timeframe?
- Can effect sizes be added (or averaged)?
- How accurate are the conclusions drawn from meta-analysis?
- How can the variability associated with each influence be evaluated?