Therapists of children with autism use a variety of methods for collecting data during discrete-trial teaching. Methods that provide greater precision (e.g., recording the prompt level needed on each instructional trial) are less practical than methods with less precision (e.g., recording the presence or absence of a correct response on the first trial only). However, few studies have compared these methods to determine if less labor-intensive systems would be adequate to make accurate decisions about child progress. In this study, precise data collected by therapists who taught skills to 11 children with autism were reanalyzed several different ways. For most of the children and targeted skills, data collected on just the first trial of each instructional session provided a rough estimate of performance across all instructional trials of the session. However, the first-trial data frequently led to premature indications of skill mastery and were relatively insensitive to initial changes in performance. The sensitivity of these data was improved when the therapist also recorded the prompt level needed to evoke a correct response. Data collected on a larger subset of trials during an instruction session corresponded fairly well with data collected on every trial and revealed similar changes in performance.