He says 'effect sizes' are much the best way of answering the question 'what has the greatest
influence on student learning'. An effect-size of 1.0 is typically associated with:
* advancing learner's achievement by one year, or improving the rate of learning by 50%,
* a correlation between some variable (e.g., amount of homework) and achievement of
approximately .50.
* average students receiving that treatment exceeding 84% of students not receiving that
treatment.
* A two grade leap in GCSE, e.g. from a C to an A grade.
An effect size of 1.0 is clearly enormous! (It is defined as an increase of one standard deviation)