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[quote=Anonymous]New in the Q&A for the common lottery. Sounds just like the process we ultimately came to in the other thread on the common lottery. (Thought I would start a new thread, since that one was so long.) Notably, there is nothing here about a process similar to New Orleans, where there are trades made so that if I get into A but ranked B higher and you get into B but ranked A higher, we switch and both get into our top choice school.

Here is the info:

http://www.myschooldc.org/faq/#common-14

How does the lottery matching algorithm work?

The My School DC lottery is designed to match students with the schools they want most, and maximize the number of students who are matched. The matching algorithm is the computer program that runs the lottery. It is a deferred acceptance model that was developed specifically for My School DC by the Institute for Innovation in Public School Choice (IIPSC) and is based on the Nobel Prize-winning work of economist Al Roth of Stanford University. IIPSC also developed the lottery algorithms for New Orleans and Denver and is currently working with Philadelphia and Newark.

The two most important things to know about the algorithm are:

Because of the way the algorithm works, students who rank schools on their application according to their true choices have the best chance of being matched to the schools they most want to attend.

Students who apply early get no advantage in the matching process.

For all schools except DCPS specialized high schools, the algorithm follows this process.

The matching algorithm assigns each student a random lottery number and attempts to match each student with his or her first choice first, then his or her second choice, and so on. A student’s ranking of schools (the order a student puts schools on his or her application) is critical because the matching algorithm attempts to match each student with his or her first choice first, then his or her second choice, and so on. However, when the matching algorithm is comparing two students who have applied to the same school, the decision is based on two criteria: (1) each student’s preferences at that school (e.g., sibling preference); and (2) if there is no difference in preferences, each student’s randomly assigned lottery number. The students’ rankings of the schools are not a factor at that point in the process. This is why the system is strategy-proof — and why students are best served by ranking schools according to their true choices (the school they most want to attend first, then their second choice, and so on).

Each student is waitlisted at every school he or she ranked higher than the school to which they were matched. (It is possible for a student to be waitlisted at every school on his or her list if they are not matched.) Siblings who apply to the same schools also are waitlisted at any school where one of their siblings is matched.

The six DCPS specialized high schools admit students based on specific criteria. Each of the specialized high schools identifies which applicants meet their specific minimum requirements, and then each school determines the order of priority among that group. The matching algorithm uses the process described above: It attempts to match each student with his or her first choice first, then his or her second choice, and so on. (The student’s ranking may include any combination of DCPS schools, public charter schools, and DCPS specialized high schools.) However, when the matching algorithm is comparing two students who have applied to the same specialized high school, the decision is made based on the school’s order of priority for the applicants.
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