There is a preponderance of evidence that feedback is a powerful influence in the development of learning outcomes. Two findings from the many meta-analyses relating to
the effects of feedback are most fascinating-the average effects of feedback are among
the highest we know in education, and feedback effects are among the most variable in
their influences. From a review of 12 meta-analyses that have included specific information on feedback in classrooms (based on 196 studies and 6972 effect-sizes) the
average effect-size was d = 0.79, which is twice the average effect (Hattie, 2009). This
places feedback among the top 10 influences on achievement. The variance of effects
was, however, considerable, indicating that some types of feedback are more powerful
than others (Kluger & DeNisi, 1996). It appears that merely prescribing lots of feedback does not imply that learning will take place, as one has to take into consideration
the differential effects of feedback on learning as well as learners.