Valid tests are tests that measure what it ought to measure. Valid is synonymous to accurate. Reliable tests are tests that yield the same result no matter what. Reliable is synonymous to consistent.
Our professor asked us how valid tests are more important than reliable tests. A great illustration of these two principles is a weighing scale. A reliable weighing scale will give you the same weight no matter the time of the day you weigh. If it is broken though, it will give you a consistent weight reading, but not your correct weight. A valid test gives you your correct weight.
I failed to answer that question correctly in the essay part of the exam. As I was walking home, 10 minutes after I have submitted my test paper, the answer came to me.
Malcolm Gladwell on privilege: rich people have lots of chances (failed grades, traffic tickets) while poor ones are only given a single chance and if they screw it, they lose it altogether.
Basics of Assessment