Tuesday, March 31, 2009

Welcome to San Francisco

The current San Francisco Student Assignment System could use some improvement. We're in luck! The San Francisco Unified School District is working on redesigning it!

I've decided to try and help out. On my first post, I'm going to share some of the resources I've found regarding the redesign:
Finally, here are some things you may want to know about the assignment process, as it pertains to kindergarden:
  • Each student has a Diversity Profile which consists of 4 binary digits (1 of 16 profiles). The digits are:
  1. English as a primary language
  2. Attended Kindergarden
  3. Socioeconomic status
  4. Extreme Poverty
  • Each school is attempting to maximize diversity by aiming for 50% ones and 50% zeros for each Diversity Profile digit. They compute a Computed Diversity Index which is equal to the sum of percentage of 1's squared, plus the percentage of 0's squared for each binary digit.
  • Each school has an initial Computed Diversity Index based on some students that are pre-assigned with sibling preferences and special program needs.
  • Students are allowed to choose up to 7 schools on their application, ranked in order by preference.
  • Schools fill empty seats from those who applied in the school's attendance area as long as their exists an applicant which improves the Computed Diversity Index.
  • They use a greedy algorithm to fill the remaining seats at each school. To fill the next seat at a school - they determine which applicant will improve the Computed Diversity Index the most using attendance area, then preference rank, then randomness to break ties.
  • At this stage, a student may have been "assigned" to multiple schools. They use the student's preference to determine which school the student is assigned to. This may open up seats at the students less preferred schools. If so, they repeat the prior step to fill those remaining seats.
  • Once all of the empty seats are filled at all of the schools - some students may be left unassigned to any of their choices. The administrators try to pick a nearby school for them using some method that I could not find documentation for.

1 comment:

  1. A few points:

    I think you meant to say "attended preschool". Also, you should add a link to the spreadsheet that Dr. Adams Dudley hosts on PPSSF: http://www.ppssf.org/Enrollment/Adams_spreadsheet.html

    Based on your analysis, it seems that parents applying to an attendance zone school are given some preference. Is that preference limited to the first choice? The district's response to the grand jury report stated that 82% of applicants don't put their attendance area school as their first choice.

    In SF, demand greatly exceeds supply as many parents simply apply to popular schools, wash out and head for parochial/private schools. I don't have the numbers in front of me, but the best way to approximate that would be to take the total number of lottery applications and subtract the number who actually enroll and subtract again the number who didn't participate in the lottery in the first place.

    If it's true that demand exceeds supply, then it seems that improving the assignment system can only go so far in alleviating parents frustration with SFUSD.