Steve Sinnott, deputy general secretary of the National Union of Teachers, said employing teachers from Africa or the Caribbean to cover shortages in British schools is endangering an enrolment initiative, which aims to achieve universal school attendance by 2015.
His concerns will be raised with politicians, educationists and aid agencies, during the 15th annual conference of Commonwealth education ministers, which starts in Edinburgh on Monday.
Mr Sinnott said: "Africa needs an extra 15 million teachers to meet the 2015 target. But Africa is a great exporter of teachers.
"Most of the children who do not go to school live in Commonwealth countries. It's a legacy of the British Empire. We need to ensure the situation doesn't get worse and that the recruitment of teachers is not exploitative."
In 2001, almost 1,000 Jamaican teachers were recruited to work in Britain.
This is a significant proportion of the island's 25,000 teachers, increasing the burden on those who remain.
"If you're from a small Caribbean country, training a teacher is a big investment," Mr Sinnott said. "If the best teachers are then recruited to come and work in the UK, it's a big deal."
And, he adds, conditions for Commonwealth teachers in Britain are often inadequate. Many are given insufficient preparation, often arriving on Sunday evening and starting work the next morning. Others are not paid as qualified teachers, or are made redundant as a result of school budget constraints. The conference, which is convened every three years, invites education ministers from 52 Commonwealth countries to discuss issues of concern. This year, they will examine how to close the achievement gap between the developed and developing world A spokesperson for the Commonwealth secretariat said: "We need to recognise that well-trained educational professionals are a highly valuable resource.
This conference is an ideal opportunity for ministers to gain insights from each other, and to share ideas."