The traditional model, adopted by most of African governments for building capacity in mathematics, was that students who distinguish themselves in their undergraduate mathematics studies were offered full scholarships to study for a PhD in mathematics abroad, often in western countries. The failure of the model may be ascribed to three reasons.
First, after the economic crisis of the mid-1970s this model became very expensive and ceased to be sustainable.
Second, the model became risky since a large percentage of students didn’t return after completion of their studies.
Third, the model was insensitive to quality. Students were sent to any university that offered a PhD program in mathematics, rather than to universities with a strong program.
The sandwich model for graduate education, with alternating research periods abroad and at home, reduces the brain drain phenomenon significantly. Two organizations that adopt this model are the Swedish International Development Agency (Sida) and the International Science Programme (ISP), based at Uppsala University, Sweden.
Other models
The Abdus Salam International Centre for Theoretical Physics (ICTP) in Trieste (since 1983): The program offers a small number of visiting fellowships for outstanding mathematicians from developing countries and a diploma.
The African Institute for Mathematical Sciences (AIMS), South Africa and Senegal (since 2003): offers a Diploma with a focus on mathematics, physics and interdisciplinary topics such as computer science, biomathematics, and financial mathematics.