Waitlists in NYC school choice--early reflections on yesterday's initial announcements

Yesterday the New York City Department of Education announced a change in the school choice assignment process--I gather that after one round of deferred acceptance, they will do something else, involving interim assignments  and wait lists.  (The original design included a subsequent round of deferred acceptance, after disseminating to unmatched students a list of schools with vacancies, and eliciting new preference lists for this second round.)
The details of the new plan for the second round aren't yet clear (at least to me).

Here's the press release from the city:

Mayor de Blasio, Chancellor Carranza Announce Easier and More Transparent Middle and High School Admissions Process
August 15, 2019
Families will now have one form and one deadline for middle and high school admissions

"“We are changing the middle and high school application processes so families don’t have to go through the gauntlet just to get a placement. There will be one application round and one deadline to make everyone’s lives easier.”

“We’ve heard from families and educators that they want a simpler, more transparent, and more accessible system of school choice, and today we’re taking a step forward,” said Schools Chancellor Richard A. Carranza. “This common-sense change will make a real difference for families across the five boroughs, and improve our middle and high school choice process for years to come.”

The DOE is eliminating the second application rounds for middle and high school. The main round application process and timeline will remain the same, with middle and high school applications opening in October with a December deadline. Students will receive their offer in March. Families can still appeal for travel, safety, or medical hardships; if families have any hardship, they will be able to access in-person support at Family Welcome Centers, rather than wait to participate in a second process. The waitlists will open after offers are released and will be a simpler, clearer process for families, increasing:

• Transparency:  By knowing their waitlist position, families have a better understanding of their chances of getting into a preferred school option in the event that seats become available.
• Ease: This is a shorter process that requires less paperwork. Rather than having to complete a second application and wait weeks—often into May or June—for a second decision or offer, families will complete one process, receive one offer, and receive any additional offers based on waitlist position.
• Consistency:  Families will now have one admissions system at all grade levels, with the changes to the middle and high school process making it more similar to the elementary school admissions process. Currently the elementary school process has one round, and the middle and high school processes have two rounds with different names; now, families will not need to learn a different process each time a child applies to a new school—allowing them to focus on school options and not process."

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From the WSJ:

New York City Introduces Wait Lists for Students Unhappy With School Placements
City’s complex school-choice system, in which students hope to be assigned to a top pick, has long been daunting for many families
By Leslie Brody

"In recent years, applicants who didn’t like their middle school assignments—given in spring for entry the next September—would have to go through an appeals process. High school applicants who didn’t like their offers would have to try a second round of applications and then appeal if need be.

"Under the new Department of Education system for fall 2020, students will be placed on wait lists for each school listed higher on their applications than the schools they were admitted to. They will be informed of their positions on wait lists and may be offered seats if they open up."

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I got some emails about this. Here's my reply to a reporter...

"at this point I’m only an observer of NYC schools from a distance—I haven’t been involved in advising them for over a decade, and even then I worked only on the high school match, not anything involving middle schools.

So I don’t know anything about the current plans besides what I’ve read today ...

So I don’t have comments so much as questions.

1. How is the NYCDOE going to handle the timing of moving waitlists?  Many vacancies don’t become visible until just before (or just after) the official start of school, which means that there could be some complications right around that time, for families and schools.
2. How will students on multiple waitlists be dealt with?  Suppose a student waitlisted at multiple schools is admitted off one of them in the summer—if he or she accepts that new assignment, do his/her other waitlist positions remain?  
1. (If other waitlists have to be given up, this could be a complicated decision whether to accept a somewhat preferred school, or wait for an even more preferred one…  If other waitlist positions can be maintained, then the process may move slowly, as some students accept for one waitlisted position, and then a better one when it becomes available, and maybe another…)
3. How long will a student have to consider whether to accept a given waitlist position?

As with many questions of market design, the devil is in the details…"

and I added this in replies to followup emails asking for my thoughts on waitlists:

"I’ve always been cautious about waitlists, because some of the questions I asked you just don’t have good answers.  There’s a tension between wanting waitlists to move early and fast—to make planning easy for families and schools, and avoid disruption of the first week(s) of school, and wanting to give students the best chance at the schools they like best…"

"my colleagues and I never recommended waitlists to nyc, back at the turn of the century.:)
We thought it was important to reduce the number of “unmatched” students who had to be assigned to a school over which they  hadn’t had an opportunity to express preferences. This is why we had a second stage of the matching algorithm, in which lists of schools with still available places were disseminated to students unmatched in the first round, so that they could express preferences over these.

Another question about the new system is, how will such students now be assigned?  E.g. they might be assigned to the closest school to their home that has unfilled places.  In what order?  i.e. after some students are assigned this way, some schools will no longer have unfilled places, and students will have to be assigned to other schools.  The things I read today didn’t address that issue, but I gather that these interim assignments of unmatched students, which will turn out to be final assignments for students whose waitlists don’t move enough, will be made without having the students express preferences.

Another question about the waitlists: how will they be ordered?  According to the school priority/preferences that were used in the first round of matching?  Or perhaps unmatched students will be given preference? (that might sound attractive but I think it would be a bad idea, because it might make it seem desirable to be unmatched after the first round, which would interfere with eliciting student preferences altogether….)

My point is not to try to guess what design decisions have been made, but rather that there are lots of important decisions that have to be made to have a working system, and the initial announcements and news reports don’t reveal these. And they will have consequences.  So I hope that the system has been carefully designed."