This study has two parallel research agenda: (1) the development of social skills and pedagogical content knowledge in teacher candidates as they work collaboratively in pairs, and (2) the development of conceptual understanding and social skills in elementary school students who are taught by teacher candidates with cooperative learning orientation. The extent of pedagogical content knowledge gained from the collaborative work by the teacher candidates was compared with those working individually. The social skills gained from collaboration were assessed through the use of observation rubrics and a checklist. The same checklist was used to rate the elementary students' participation as they carried out the science activities provided by the teacher candidates. Student understanding of the science concepts in the lessons taught was assessed by a test. Results show that success, in terms of enhanced understanding and social skills development, was associated with varying levels of cognitive complexity of the lessons and higher levels of accountability. (Contains 4 tables and 1 figure.)