The Common Core of Data (CCD) file used for the frame corresponds to the 2000–2001 school year, whereas the assessment year is the 2002–2003 school year. In this two-year period, there were schools that closed, schools that changed structure (one school becoming two schools, for example), and schools that came into existence.
To achieve as close to full coverage as possible, the school sample was supplemented by sampling new schools, obtained from a sample of districts which were sent a list of the CCD schools and asked to add in any new schools or old schools that had become newly eligible for fourth or eighth grade.
Since asking every school district to list new and newly-eligible schools would have generated too much of a burden, a sample of districts was contacted to obtain a list of new schools. To represent the unsampled districts in the full sample of schools, weights for schools included in the new-school sample were adjusted to reflect the district selection process probability.