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Thousands of DC students switch schools midyear, especially at some high schools that are part of the DC Public School system. That has negative consequences both for the students who switch and the schools they enter.

A recent report from DC’s Office of the State Superintendent of Education found that over 92% of DC students remain in the same school throughout the year, based on data from 2011 through 2014. Some have hailed that as proof that the system is fundamentally stable.

But that 8% of students who move midyear is more significant than it sounds, and DCPS schools take in a disproportionate number of new students as compared to charters. In fact, many students who transfer to DCPS midyear come from charter schools. Most of the new arrivals, however, come from other DCPS schools or other states.

Students who switch schools midyear are often already at risk, and transferring only exacerbates their difficulties. They’re more likely to have low test scores and to qualify for special education than the DC population as a whole, according to the report. They’re also disproportionately low-income, African-American, and male.

Schools that take in a lot of students midyear also face challenges. If a school has established clear routines and rules, late arrivals won’t be familiar with them. Some may bring behavior problems that caused them to leave their previous school.

Teachers need to devote extra effort to bringing new students up to speed on what the rest of the class has been learning. Other students at the school can suffer as a result.

Clearly, there are powerful incentives for schools to deny admission to students after the school year has begun. But it’s also obvious that it would be a bad idea to deprive thousands of kids of any education whatsoever.

Besides, in DC, only charters have the option of turning midyear applicants away. Neighborhood DCPS schools are legally required to take all comers, whenever they arrive.

DCPS has a net gain of students while charters have a net loss

According to the report, over 6,000 students entered or exited DC schools or changed schools within DC at least once during the 2013-14 school year. Both sectors lost students during the course of the school year, but charter schools were much less likely to replace them with new arrivals. By June, DCPS experienced a net gain of 2% of its enrollment, while charter sector enrollment had declined by 5%.

Some have charged that much of the churn in DCPS is caused by students leaving charter schools midyear, voluntarily or involuntarily. The report shows that many more students do leave charters for DCPS midyear than vice versa.

In fact, over the three years studied, the number of students going from charters to DCPS was more than 12 times the number who have moved in the opposite direction. And over 30% of charters’ decline in enrollment each year was due to students transferring to DCPS.

But it’s also clear that students arriving from charters are only a fraction of the students entering DCPS schools midyear. More students switch schools within DCPS. For the three years covered by the report, 717 students on average switched from one DCPS school to another each year, while an average of 584 entered the system from charters.

And the number of students who entered DCPS from beyond DC’s borders is greater than the number of transfers from charters and other DCPS schools put together: 1,783 a year, on average.

High school students move more than others

It’s also clear that there’s more movement at the high school level than in other grades. Students in 9th grade had the highest rate of churn in 2013-14, with 12.4% switching schools. At 10th grade, the figure was 8.7%. The only other grade level with a higher rate was preschool for three-year-olds.

That’s in line with another study that found 30% of DC students switch high schools at least once. And high school is a particularly bad time to switch: a student’s chances of graduating sink by 10 percentage points each time he transfers, according to the study.

A few DCPS high schools have the highest influx of midyear transfers, according to data gathered by the Washington Post. Cardozo High School, which takes in many immigrant students, had a 30% increase in enrollment during the year. Its net gain, after offsetting the increase with students who withdrew, was 18.4% of its student body.

Other high schools, including some application-only DCPS schools, were comparatively stable, losing or gaining less than 1% of their population. Meanwhile, 16 high schools, all of them charters, had a net loss of between 3 and 22.5%.

At Roosevelt High School, which had a net gain of 8.4%, there were 487 students enrolled at the beginning of the 2014-15 school year. By May, 47 had withdrawn, but 73 others had arrived.

New students may arrive with vastly different needs. At Roosevelt, the newcomers included a 17-year-old from Guatemala who was in school for the first time since 6th grade, a 9th-grader who had left a charter after she was caught with marijuana, and an 18-year-old who had dropped out of another DCPS high school after moving into a group foster home near Roosevelt.

A change in school funding may help but won’t solve the problem

Clearly, officials need to take steps to reduce student mobility in DC. One possibility now under discussion is to change the way schools receive compensation. Currently, charter schools receive a set amount for each student enrolled on October 5th. If they gain or lose students after that date, they neither take in or lose additional money.

A system that compensates charters more accurately for the number of students enrolled throughout the year might give them an incentive to retain students. But it wouldn’t help reduce the far greater inflow of students to DCPS from other sources. And it’s not clear charters would be willing to admit a larger share of the students who arrive midyear even if they got compensated for them, given the disruption such transfers can cause.

There may be policy changes that could reduce the amount of transferring within DCPS, but it’s not clear officials can do anything about the movement across state, and even international, lines. It would help, however, if DC could at least share data about students and their movements with Maryland and Virginia.

That would allow schools here to determine the backgrounds and needs of students who enter from those states, and it would enable DC officials to understand what happens to the many students who transfer to those states’ schools from DC. That kind of data sharing is a possibility that OSSE is currently exploring, according to the report.

As the report concludes, we need more information about the underlying causes of student movement from school to school before we can try to reduce it. But even once we identify them, those causes may be hard to address.

Some have suggested, for example, that a system of school choice is part of the problem, because it’s led to a cavalier attitude about moving from one school to another. And given that students who transfer midyear are disproportionately at-risk and low-income, poverty and housing insecurity may also be driving a lot of the mobility.

So it’s likely that student mobility will be a fact of life at many DCPS schools for the foreseeable future. It would make sense to develop specific programs to help integrate new students at schools that receive large numbers of midyear transfers, as Cardozo has done for immigrant students.

And when we’re comparing one school’s level of achievement to another’s, we should take into account whether a school has been acquiring additional challenging, and possibly disruptive, students—or whether it’s been losing them.

Cross-posted at DC Eduphile.

Natalie Wexler is a DC education journalist and blogger. She chairs the board of The Writing Revolution and serves on the Urban Teachers DC Regional Leadership Council, and she has been a volunteer reading and writing tutor in high-poverty DC Public Schools.