This study aimed to compare the results of conventional methodology and real-time polymerase chain reaction (PCR) for acid-producing bacteria and identify the appropriate method for caries activity testing. Methods: Oral examination and caries activity tests, such as the CRT ® Bacteria test and modified Snyder test, were conducted on 33 middle school students in Cheongju, South Korea. Pearson correlation analysis was subsequently performed with a significance level of 5%. Results: The amount of Streptococcus mutans determined using the CRT ® Bacteria test was highly correlated with the decayed teeth (DT) index (R=0.570, P<0.05); decayed, missing, and filled teeth (DMFT) index (R=0.376, P<0.05); and dental health capacity of the first permanent molar (R=-0.395, P<0.05). The amount of Streptococcus mutans determined using real-time PCR was significantly associated with the DT index (R=0.528, P<0.05), DMFT index (R=0.369, P<0.05), and dental health capacity of the first permanent molar (R=-0.426, P=0.013). Conclusions: There was a significant correlation between the amount and the type of bacteria between the CRT ® Bacteria test and real-time PCR; therefore, these tests were found to be more appropriate to determine caries activity than the modified Snyder test. This study suggests that realtime PCR is a better technique for detecting caries activities than conventional techniques, such as the CRT ® Bacteria test and modified Snyder test, because it is easy to use and provides accurate results.