To preliminarily validate the Monitoring Instructional Responsiveness-Reading (MIR-R) for use in low-income settings, data were collected from 147 students from first through fifth grades who were primarily from low-income families. Data from three MIR-R components (Total Words Read, Ideas Attempted, Ideas Correct) and three related dependent measures (i.e., Test of Silent Contextual Reading Fluency [TOSCRF], Test of Silent Word Reading Fluency [TOSWRF], and Gray Silent Reading Test [GSRT]) were obtained across two time points (i.e., Time 1 and Time 2) in the same setting to address test-retest reliability and concurrent validity. Results showed (a) stability of the three MIR-R components scores over time, (b) strong correlations (p < 0.05) between the MIR-R Total Words Read and Ideas Attempted and TOSWRF and TOSCRF, and (c) strong associations between MIR-R Ideas Correct and TOSCRF, TOSWRF, and GSRT in Time 1 and Time 2. Because these results showed strong associations between MIR-R and established measures of reading and because MIR-R can be administered in only 3 min, it may provide an efficient operationalization of student progress. Additional implications were discussed.