A 14-week course program was designed to investigate pre-service teachers' noticing skills and scaffolding practices. Six pre-service teachers were matched with a pair of sixth grade students to observe and scaffold students' mathematical understanding while they were working on the given tasks. Data was collected through pre-service teachers' own recorded videos of implementation of tasks, their written reflections about the implementations, videos of group reflections before and after the implementations, and students' written work. The analysis of data revealed that pre-service teachers mostly noticed students' errors and strategies during their interactions with students, they attended important instances about students' thinking and justified their reasoning for their comments in their written reflections. However, while interacting with students, they usually used low level scaffolding practices such as asking for clarification, explanation, and justification rather than attempting to elicit students' thinking and improve their understanding.