This study examined technical features of slopes produced from curriculum-based measures (CBM) of beginning writing. Eighty-five first-graders completed weekly sentence copy, picture-word, and story prompts for 12 weeks. After 12 weeks, testing revealed alternate-form reliability and criterion validity of CBM scores generally similar to those found in previous research. Examinations of group- and individual-level slopes indicated 8 or 9 data points are needed to yield reliable and stable slopes. The picture-word task appeared most sensitive to growth in brief periods, yielding slopes that were significantly greater than 0 within 4 weeks. Research directions and recommendations for monitoring progress of beginning writers are discussed.