Identifying differences can sometimes begin with clarifying similarities. A similarity between the Situational Language Teaching, which began in the 1930s, and the audio-lingual method, which began in the 1950s, is that they both use Structuralism as the foundation for language learning practices.
In contrast, the direct teaching method, which was developed in 1900, does not use Structuralism as the foundation for language learning practices. It was instead a response to the Grammar-Translation (translation from one language to the other) method of language teaching.
Since the situational and the audio-lingual methods are linked to Structuralism, they both rely on behavioralism and emphasize habit-formation, correctness, and contextual and cultural clues. One way these two differ is in their objectives.
The situational method has as an important objective proficiency in the four basic language skills: listening, speaking, reading, writing. In contrast, the audio-lingual method omits those as objectives but keeps the two objectives common to both methods: accurate pronunciation and grammar and quick, accurate speech responses.
The third objective of the audio-lingual method, which differs from the other objective of the situational method, is knowledgeable vocabulary to use with correct grammar patterns. In contrast, the final objective of the situational method is automatic control (done without thinking) of basic language structures and sentence patterns.
The biggest pedagogical difference between the situational and audio-lingual methods is that the first (situational) emphasizes language learning in situations in which language elements are or could be actually used, while the second (audio-lingual) emphasizes heard, then repeated and drilled model dialogues.
Situational method teaches for language production if real situations. Audio-lingual method teaches for acquired dialogs models that fit various topics. Direct language teaching requires immersion in the new language targeted, without depending on the mother-language, to learn the target language.
The theoretical foundation of the direct method is that second languages must be learned in the same way that the first language was learned. Critics point out that conditions at the time of second language learning are very unlike conditions at the time of first language learning.