Whether in flight from conflict, with the hope of building a better life, or to seize a social or economic opportunity, people have been crossing borders for as long as there have been borders to cross.
But how well are school systems adapting to increasing numbers of immigrant pupils? The OECD last month published a Pisa in Focus report on the issue, analysing findings from the 2009 Programme for International Student Assessment report.
It found in most countries that immigrant pupils lag behind native pupils in performance and, in many, the difference is considerable. However, Australia, Belgium, Canada, Germany, New Zealand and Switzerland have been able to narrow, and in some cases close, this performance gap.
The bottom line, according to the report, is that school systems can nurture immigrant pupils' full social and economic integration into their adopted country by identifying the obstacles to high performance that are particular to immigrant pupils and developing programmes that are tailored to meet these pupils' needs.
On average among OECD countries, the proportion of pupils with an immigrant background grew by two percentage points between 2000 and 2009.
Immigrant pupils represent more than 5 per cent of the pupil population in 13 OECD and partner countries and economies that participated in Pisa 2009.
Belgium and Switzerland closed the gap by nearly 40 score points during that period, the equivalent to one year of schooling, even though native pupils still outperform pupils with an immigrant background by 68 score points in Belgium and by 48 score points in Switzerland.
Switzerland has also been able to reduce the performance gap despite the fact that the percentage of pupils with an immigrant background rose during the period.
In Australia, pupils with an immigrant background perform better than native pupils. In Canada, immigrant pupils performed as well as native pupils in 2009, and they represent a large - and growing - proportion of the pupil population.