Students from urban high schools are usually faced with adverse environmental factors in their pursuit of academic success. These factors make learning more challenging and may confound the measurement of academic performance itself. This study explores how one such factor, ambient noise, affects the measurement of mathematics achievement. Overall, about 40% of students were bothered by noise during testing. The more bothersome the noise is, the lower the math score tends to be. Noise coping explains about 10% of the test score difference, comparable with that by grade point average. These findings indicate a clear association between noise and math achievement measurement.