The sudden arrival of immigrant pupils can have a silver lining for schools. A primary head in the east of England once told me that she had started nudging her local authority to send her any Polish children who moved to the area. Her school was predicted to miss its maths test targets, she explained, so she reckoned her best hope might be the last- minute addition of a few highly numerate Polish boys.
In most cases, however, an influx of new pupils is a problem. High pupil turnover presents challenges for teachers. And the work staff do to help those children catch up and settle in frequently goes unrecognised. There may be a comment about pupils' high levels of mobility buried in a school's Ofsted report, but it is tricky for teachers to raise the matter in their defence when league tables are published or politicians attack low-performing schools.
If even a small proportion of pupils fail to meet a test target, schools can be publicly lambasted for failing to give all their students a proper education. Yet the pupils who fail may have only spent a brief period of time at that school. Conversely, all the work that same school does to help another pupil become an academic star goes uncounted if the child's family moves in their final year.
Teachers in areas with high levels of recently arrived immigrants face the most obvious challenges - and have the added difficulty that their new pupils may speak little English. But it would be a mistake to see high pupil mobility just as an immigration issue. Many schools affected by it have students who move for other reasons, whether it is because their families are being shifted between temporary housing, or are members of the armed forces or the travelling community.
Luckily, the schools with the greatest experience of this challenge have not responded by grumbling. Instead, they have developed their own successful techniques to ensure that new pupils settle in fast. By following their lead, more schools may grow to regard new arrivals as less of a hindrance. But whether it is right to start talent-scouting different nationalities to boost test scores is another matter altogether.