This paper offers guidelines in the consideration of an open or closed classroom-observation system. Factors in the definition of an observation approach include target, timing, focus, topic of observation, and data-collection system. Because there are advantages and drawbacks to any classroom-observation system, the following factors should be considered when deciding whether to use an open or a closed observation system: the purposes of the observation, the amount of time and staff available to collect and analyze the data, and the extent to which the behaviors and event under study are clearly defined. Whatever observation approach is used, evaluators other than the researcher should be able to replicate the lesson, teaching context, and sequence of activities. Analysis, evaluation, and utilization of data should be conducted after the observation. The qualitative data provided by an open-ended approach can be more helpful in understanding and justifying decisions after the observation is conducted. One table is included. (LMI)