Effect sizes below d=0.40 aren’t ignored however a decision has been made to not look at what works (d=0.00 – 0.40) but what works best (d>0.40). Ninety percent of all effect sizes in education are positive (d > 0.0) and this means that almost everything works. The effect size of d=0.40 looks at the effects of influences in achievement in such a way where we can notice real-world and more powerful differences. It is not a magical number but a guideline to begin discussion about what we can aim for if we want to see student change.

### 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?