The school base weight for a sampled school is equal to the inverse of its probability of selection. The computation of the school base weight differs by whether the school was an original, new, or a substitute school.
The school base weight for an original school is equal to the inverse of its probability of selection from the NAEP public or private school frame.
The school base weight for a new school is equal to the inverse of its overall probability of selection, which is the product of two components:
A school that takes the place of a refusing original school is known as a "substitute school." A substitute school is treated as if it were the original school that it replaced, and so is assigned the school base weight of the original school.