The purpose of this study was to assess children's understanding of plant nutrition. The research was done on a sample of secondary school pupils in the age range of 16 to 19 years in two senior secondary schools in Botswana. The sample contained 137 senior secondary pupils all in their final year of study. These children were above average ability. The children were given a test on plant nutrition composed of two parts namely forced and free responses which were based on the Botswana senior secondary school biology syllabus. After the administration of the test to the pupils, interviews were conducted to give children the opportunity to explain their answers. The majority of children experienced little difficulty in providing accepted ideas about plant nutrition. However, analysis of children's responses showed that mistakes were often made in the process of where plants make food rather than in the process of how plants make food. In conclusion, suggestions and recommendations were made with the hope that they would help teachers teach plant nutrition in a meaningful way. (Contains 3 tables.)