Educators, school psychologists, and other professionals must evaluate student progress and decide to continue, modify, or terminate instructional programs to ensure student success. For this purpose, progress-monitoring data are often collected, plotted graphically, and visually analyzed. The current study evaluated the impact of three common formats for visual analysis (scatter plots, scatter plots with trend lines, and scatter plots with trend and aim lines) on the decision accuracy of 52 novice analysts. All participants viewed 18 time-series graphs that depicted student growth on a continuous metric (e.g., oral reading fluency). Participants rated each graph as depicting substantial progress, minimal progress, or no progress. The magnitude of the true slope for each graph was fixed to 3.00 (substantial progress), 0.75 (minimal progress), or 0 (no progress). Inferential analyses were used to determine the probability of a participant correctly identifying different magnitudes of trend in the presence of different visual aids (no visual aid, trend line, and trend line with aim line). The odds of correctly identifying trend were influenced by visual aid (p < 0.01) and trend magnitude (p < 0.01). The addition of a trend line resulted in a sharp increase in the probability of making a correct decision. Graphs depicting minimal progress reduced the probability of a correct decision.