Research by their former headteacher shows their peers excelled in America and Canada but in England, where the majority sought refuge, they became disaffected.
Gertrude Shotte believes teachers' low expectations of black and refugee children is the main cause. "The cream of the crop came here," she said.
"But the majority did poorly."
More than 7,000 people fled Montserrat after the Soufriere Hills volcano erupted, killing 19 and leaving thousands homeless. More than 6,000 came to the UK.
Dr Shotte came to London in 1997 after her primary school was forced to close. The majority of her 180 pupils, aged five to 11, and their families, joined her believing the education system was similar to Montserrat's.
Dr Shotte's research, which forms a PhD thesis for London's Institute of Education, is based on a five-year investigation of 40 pupils' experiences in London.
Many were shocked at what they found: "What teachers here accept is totally unacceptable in Montserrat," said one 16-year-old girl.
They found lessons unchallenging. Five students labelled as A-grade in Montserrat were placed in classes a year below their level to repeat areas of the curriculum. Pupils said teachers would ignore them and treated them as if English were their second language.
Dr Shotte said the pupils' main problems were institutional racism and teachers' poor expectations.
Julie Davies, secretary of Haringey National Union of Teachers, said it was understandable the families felt disappointed with schools in a deprived part of London. But she said it was "absolutely dreadful" to claim teachers were failing the pupils.
A spokeswoman for the Association of London Government, which has launched a report with more than a dozen measures to improve the education of London's ethnic minority pupils, said Dr Shotte's findings matched some of its own research.