The difference in 5th and 6th grade Teaching Year data enrollment numbers is the result of a small number of students who were retained and a somewhat larger number of students who either left to go to private school or left the state (and in a number of cases, the country) . If you look at "Testing Year" data which includes the 6th graders who randomly filled those empty seats and were with BVP for a month before taking the test, the proficiency percentages are slightly lower but still impressive: 86% math, 80% reading. I don't know how BVP's mobility rate compares to the district.
I don't know how many students were retained, and generally this would be obscured by the students retained by the previous year's sixth grade class, but based on Magee's statement it is less than half of the unaccounted for seventeen students. Let's just note that a high retention rate is part of the "no excuses" model BVP embraces:
Democracy Prep Harlem, the first school in a new network that plans to open more schools in New York and Rhode Island, is a charter that subscribes to the "no excuses" principle common at charters, meaning everyone, from students and parents on up, is held accountable for their performance and must pay consequences if they don't measure up. Unlike many charters, Democracy Prep, a middle and high school, has an outsized population of special-education students. Seth Andrew, the school's founder, says students at the school are far behind when they arrive in sixth grade. Last year, more than 20 percent of the sixth-grade class was held back. "The reason that charters exist is to help remediate for traditional public schools that are not teaching students to read, write, or do math, and that's not a one-year job," he says.
Of course, BVP may not really be able to hold to this approach in the long run -- the scrutiny of suburban schools is much greater, as we can see from this conversation.
Provplan has a great resource on mobility in Providence urban districts (from 2007 - 2008) which states that about 13% of the Central Falls school district's student population left the state during the course of the year. Pawtucket was around 8%. On the other hand, you don't see teaching/testing year gaps of this size in similar charters like The Learning Community or in, say, Central Falls middle school, so there still may be some inconsistency in how this is being measured or exactly what's happening. I'd also note in passing that I'd love to know exactly how much of CFHS's 15% grad rate increase was attributable to better tracking of leavers getting more kids off their books.
It may also be true that there's a somewhat larger slice of parents who chose BVP as an alternative to private school and decided not to stay. That is, if their alternative was other public schools, they'd still show up as "teaching year" students, but perhaps this population is more likely to go to a private school as their choice. Certainly BVP is marketed more like a private school than most urban charters (e.g., on sports talk radio).
I don't think any of this is particularly nefarious. It is just odd. BVP is a peculiar school, and nobody knows what it path will be. I'm certainly curious. It is already clear that there will never be another school quite like it in Rhode Island, as RIMA and RIDE have disavowed most of its most distinctive features.