Research has consistently demonstrated the importance of providing an appropriate level of challenge, called the instructional level, within curricular material. Although the instructional level is a generally well-defined and researched construct, much less data exist on the acquisition rate (AR) component of an appropriate level of challenge. The current study used curriculum-based assessment to assess the AR of five fourth-grade students diagnosed with a reading disability and taught each 20 words from the Esperanto International Language over two sessions (10 each session). Students were observed during instruction, and the number of demonstrated off-task behaviors was converted to a mean rate of off-task behaviors/minute. Comparison of pre- and post-AR data showed that each student demonstrated an increase in off-task behaviors while rehearsing the word that immediately exceeded his or her AR. Implications for practice and suggestions for future research are discussed.