Sluggish cognitive tempo (SCT) is a construct that some researchers believe may be extremely useful in understanding the inattentive subtype of attention-deficit/hyperactivity disorder, and may even help define a completely new disorder. However, the construct of SCT is as yet inadequately operationally or theoretically defined. The authors took the first steps toward developing an empirically supported measure of SCT in children. In Study 1, potential items to measure SCT were identified from a literature review, content validity of the items was evaluated by a group of experts, and a preliminary set of SCT items were selected. In Study 2, ratings completed by parents and teachers of 335 children (ages 4-13) were used to further develop and evaluate the SCT items by computing factor analyses, item-level analyses, reliability analyses, and preliminary validity analyses. The final SCT scale (14 items) produced a total scale score and 3 subscale scores: Slow, Sleepy, and Daydreamer. These scales were constructed with good content validity and were found to have strong reliability. Future directions include replication, extension into a clinical population, and further examination of validity. (Contains 6 footnotes and 7 tables.)