The superordinate problem that the Threshold Project addressed is the nature of the language and learning difficulties that South African Standard 3 (Std 3) children experience when they change from their mother tongue to English as a medium for instruction. The primary focus of the Threshold Project work in 1987 was on a section of the South African Std 3 general science syllabus entitled plant structure, growth, and reproduction. As an aid to curriculum construction, this relatively non-technical report describes learning theories, reviews the educational research, and reports the results of pre and posttests to assess content knowledge and science process skills. Some of the major conclusions of the report are summarized as follows: (1) Research in the field of alternate conceptions in the South African context needs to be done; (2) a teacher-centered enquiry approach or transition model is the recommended form of instruction; (3) students whose native language was Setswana and were taught in the conventional way in English demonstrated no real learning gains; (4) students taught in a traditional manner in Setswana demonstrated large learning gains and (5) after being taught in the "transitional way" in English, students were able to demonstrate some learning gains. It was concluded that the policy of effecting a complete transition to English in Std 3 is hindering the learning of the children. (PR)