Throughout the year, Sadie observes her students and makes notes on their progress. She takes videos of her students solving problems and analyzes them in order to develop strategies to maximize their success. Sadie is engaging in:

formative assessment

Explanation:

Formative assessment can be described as the number of different ways which teachers use to make in process evaluations of the academic progress of children. By looking at these evaluations, the teachers can get ideas to incorporate some better methods for making a particular concept more easier and clear for the children.

One such method of formative assessment was being used by Sadie. She took videos of her students to observe and make notes on their progress.