The first round of the study began in 1989/1990, and questioned the still-pregnant mothers about general demographic characteristics, and the conditions of the pregnancy. After further rounds of assessments and surveys at birth and six months, data was obtained on an annual basis. The question in the yearly suveys cover a broad range of topics, touching on both the physical health and development of the child, his or her environment, education, nutrition, socioeconomic class, and cognitive development. Later surveys also monitor each subject's opinion on politics, Africa, and other social opinions.
The study is unique source of information for major policy decisions in the South Africa, especially due to the absence of other data. Information on children's recognition of cigarette brands, for example, was used by the Minister of Health from 1997 to 1999 to push forward progressive tobacco legislation, preventing public advertising and the sale of cigarettes to minors. The early age of school entry revealed by longitudinal data was used by the Ministry of Education in 2004 to legislate a minimum age for school enrolment.
As a longitudinal study, one of the major criteria by which one may judge the Birth to Twenty study is by the number of subjects for whom data is obtained in each round, or the attrition rate. One of the difficulties encountered by the Birth to Twenty is that many subjects move out of the area, and can no longer participate. Nevertheless, the study has quite consistently obtained data from between 50% - 65% of the original cohort of 3,273. In 2005-2006, for example, data was collected from 2,100 subjects, or 64%.