OK, we give a pretest in the fall and then the same test in the fall and the difference in scores shows what the student learned. We are to aim for a 30 percent increase EXCEPT that it is measured in what I consider an odd way. To my way of thinking, if Amy earned a 30 on the pretest and a 40 on the test, she has achieved a 30% growth.
If she earned a 30 on the pretest, that leaves 70 to make a 100. 30% of 70 is 21, so Amy would need to earn a 51 (30 + 21) to achieve a 30% growth.
Obviously, the higher your initial score, the less you have to make on the post test for growth, so this is scewed against the low achievers.