It is now a trend to use "they" to be politically correct when using general terms. Instead of saying, "When a teacher suspects wrongdoing, he is obligated to report it," people substitute "they are." It's probably less awkward than always using the "he or she" expression, but English doesn't really have a pronoun that covers both genders equally, and many people have become very sensitive over using "he" as a general pronoun.
Some people are insistent that language be totally inclusive, but until we come up with a gender-neutral pronoun, writing around gender pronouns can get downright awkward. At least, saying "he or she" with a singular verb is grammatically correct, which, to me, is paramount.