Several considerations need to be made when monitoring student reading progress using Curriculum-Based Measurement (CBM): the instructional level of the student, the type of goal set for the student, and the material selected. Although research has demonstrated that long-term goals based on the student's instructional match are most sensitive to student gains, there have been few studies investigating whether probe material should be selected from material in which the student is currently instructed (i.e., similar material) or from material in which the student is expected to be instructional after one year (i.e., challenging material). The purpose of this study was to determine whether similar material or challenging material would be the most sensitive for progress monitoring of student oral reading fluency. The oral reading fluency of 20 students reading on a second grade level was monitored concurrently with similar and challenging material. The students' progress was monitored twice a week for 8 weeks. The results of this study suggested that the measures were equally sensitive. However, both types of measurement appear to have significant error associated with the data.