This report reviews the development, piloting, and preliminary results from the large-scale field trial of the TASK Instrument (see cpre.org/task). In the first section, we review the need for an assessment of teachers’ capacity for learning trajectory-oriented instruction and the theoretical foundations that inform our work. We then describe the instrument and its development. Next, we detail the scoring process and the training of raters. The final section contains the analysis of the large-scale field trial conducted in 2012–13. We conclude with some directions for future work with this instrument.