ABSTRACT
A lifespan developmental systems perspective, which helps resist the urge to ignore, simplify, or reduce the target system, allows to use the problem of developmental measurement equivalence as a set of instructions about how to create multiple lines of sight into the phenomenon. The issue of equivalence is at the heart of discussions about bias in testing. Controversy swirls around tests with consequences—like ones that decide whether students will get into special services or advanced placement courses or college or graduate school. Researchers typically cope with the problem of measurement equivalence by staying inside the age groups circumscribed by their key measures. Whatever the strategy, the take-home message is that the “problem” of developmental equivalence can be turned into an asset when researchers use it as a signpost, telling them, “Here is some qualitative development”—and urging them not to turn back.
