A data frame with 7230 observations on the following 12 variables.
    - schoolid
- a factor of school identifiers 
- childid
- a factor of student identifiers 
- year
- a numeric vector indicating the year of the test 
- grade
- a numeric vector indicating the student's grade 
- math
- a numeric vector of test scores on the IRT scale score metric 
- retained
- a factor with levels - 0- 1indicating if
    the student has been retained in a grade.
 
- female
- a factor with levels - Female- Maleindicating the student's sex
 
- black
- a factor with levels - 0- 1indicating if
      the student is Black
 
- hispanic
- a factor with levels - 0- 1indicating if
    the student is Hispanic
 
- size
- a numeric vector indicating the number of students
      enrolled in the school 
- lowinc
- a numeric vector giving the percentage of low-income
      students in the school 
- mobility
- a numeric vector