Detroit's Peer Teachers as Mirrors and Monitors Project is intended to validate cost effective methods for increasing Academic Learning Time (ALT) for students in grades one through four. A major problem in this research effort has been the design of valid and reliable measures of the components of ALT. One very important component of ALT is student and teacher use of time. This presentation addresses some of the issues involved in measuring student time-on-task, and teacher's use of time with students. Observation methods which produce valid and reliable data without interrupting classes or threatening teachers (too much) are discussed. Samples of observation instruments developed by the project are included, along with issues related to training observers and the establishment of definitions of behaviors to be observed so as to produce high inter-rater reliability. (Author)