Single-case designs substantiate the effectiveness of interventions for people with disabilities and other populations through the repeated measurement of behavior over time. Consequently, employing accurate and reliable systems of measurement is critical to the validity of single-case designs. Much of the data in single-case research are collected through systematic direct observation. Direct observation often involves the use of time sampling, wherein an observer indicates whether a behavior occurred during a specific period. Although scholars have highlighted the potential for time sampling to distort the results of single-case design, targeted reviews indicate time sampling continues to be used in literature involving people with disabilities. The current study reviews literature from the field of special education, in which single-case designs are frequently used to evaluate the efficacy of practices. Using a large, representative sample of 1,425 randomly selected single-case design articles from 33 special education journals, we coded articles to determine the type and features of measurement systems employed by researchers. Findings indicate one-fifth of articles feature some form of time sampling. In addition, time sampling is more prevalent in journals pertaining to individuals with emotional/behavioral disorders. A discussion of implications for research quality follows an overview of results.