**Core Concept**
Lancefield grouping is a method used to classify beta-hemolytic streptococci based on the presence of specific antigens present on the cell wall. This classification is crucial for identifying the causative agent in various infections.

**Why the Correct Answer is Right**
The Lancefield grouping is performed using the CAMP (Christie, Atkins, and Munch-Peterson) test, which detects the presence of a specific antigen. The test involves mixing a test strain with human serum and a known Lancefield group A strain. If the test strain produces a zone of beta-hemolysis, it is considered positive. The reaction is due to the presence of a specific carbohydrate antigen on the cell wall of the test strain, which reacts with the antibodies present in the human serum and the Lancefield group A strain.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the CAMP test is not used for identifying other types of streptococci, such as group B streptococci, which have a different mechanism of action.

**Option B:** This option is incorrect because the Quellung reaction, which is used for identifying pneumococci, involves the use of specific antibodies that react with the capsular polysaccharide of pneumococci, not the cell wall antigens of streptococci.

**Option C:** This option is incorrect because the Coagglutination test is used for identifying various pathogens, including streptococci, but it is not the primary method used for Lancefield grouping.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that Lancefield grouping is crucial for identifying the causative agent in streptococcal infections, such as rheumatic fever and post-streptococcal glomerulonephritis.

**Correct Answer:** C.