Most grammar textbooks give students sanitized, simplistic sentences for exercises. Thus in an exercise on prepositional phrases (if they ever get to prepositional phrases), these textbooks will not include in an exercise a sentence in which "after" is used as a subordinate conjunction. Similarly, in an exercise on subordinate clauses, they will not use "after" as a preposition. In learning to deal with real texts, however, students need to learn to make the distinction. At this level, students need simply learn that if whatever answers the question "What?" after a "preposition" is a sentence, then the construction is not a prepositional phrase. You can tell them that it is a subordinate clause, and that they will learn more about subordinate clauses in KISS Level Three, but the focus at this point should be on their ability to identify the prepositional phrases. 
 

Suggested Directions for Analytical Exercises 1. Place parentheses ( ) around each prepositional phrase. 2. Underline every finite verb twice, its subject(s) once, and label any complements (“PA,” “PN,” “IO,” or “DO”).

Probable Time Required      You can skip this altogether, or you might prefer to show your students one exercise, or you can have them do two or more exercises.

Preposition or Subordinate Conjunction?

Instructional Overhead