For children who changed schools between base-year kindergarten and spring first grade,
a random 50 percent subsample were flagged to be followed for data collection. In selecting
these students, the three primary strata were self-representing primary sampling units, non-selfrepresenting
primary sampling units that had been selected for fall-first grade subsample, and
non-self-representing primary sampling units that had not been selected for fall-first grade.
Within these strata, schools were grouped by original public, original private, freshened public,
and freshened private. Within this, schools were stratified by whether the school participated in
the base-year study and were then arranged in original selection order. Then equal probablity
sampling methods were used to obtain the 50 percent sample. Basically, each base-year school
had a 50 percent chance of its transfer children followed during the spring of first grade