“After adjusting for student characteristics,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Adjusting for characteristics????
Whoa! Plenty of opportunity for mischief there!
Not really.
The student characteristics they used were gender, socioeconomic status (as measured by eligibility for free or reduced lunches), race/ethnicity, whether the students had disabilities (including learning disabilities, retardation, etc.), and whether the student spoke English well or was just learning the language.
I believe they also adjusted for whether the school was rural or urban, which state it was in (since different states have different standards and differing curricula), experience of the teacher, etc.
You can read the executive summary of the report here.