1. What is meant when we say that student test scores are distributed in a bell curve? How is effect size interpreted in terms of instructional design and practice?
Statistically, students' achievement scores tend to be distributed according to the well-known "bell curve," also known as normal distribution. In other words, the majority of scores are clustered around the mid-point of the scale, or distributed symmetrically around the mean, with fewer scores occurring as the distance from the mean increases according to a specific mathematical equation. Standard deviation is the measurement of how scores are clustered or dispersed in relation to the mean. It is a measure of variability, something akin to an average distance from the mean.
Normal distribution has a range of about three standard deviations above the mean and three standard deviations below the mean. In graphic terms, envision a bell-shaped curve divided in half at the highest part (the mean score), then add two more vertical lines at equal intervals on each side. About 68 percent of the population can be expected to lie within the first ...
This solution explains what it means for students test scores to be distributed in a bell curve and how the effect size is interpreted in terms of instructional design and practice.