In teaching my ASVAB prep course, I make sure to emphasize the different types of author’s purpose when covering Paragraph Comprehension.  I spend much more time on ASVAB math help than Paragraph Comprehension review, but I do make sure to emphasize author’s purpose in my classes.  I remind my students of the word “pie” to remember the main types of author’s purpose.  P stands for persuade.  I stands for inform.  E stands for entertain.  As someone who tutors for the ASVAB, I see that many students confuse author’s purpose with author’s tone.  Author’s purpose is  why the author wrote the piece, while author’s tone is the attitude that author had in the piece.