"Los maestros se preocupan por los estudiantes."
Translation:The teachers worry about the students.
I believe 'the teachers are worried' would have to be 'los maestros están preocupados' because in that example the verb is estar (to be/are in English) and worried is an adjective. In English, worry and its forms can work as noun, verb, and adjective, many of which overlap (i.e. worried can be past tense verb or an adjective, worry can be a noun or present tense verb). In Spanish however, it seems that the adjective is distinct from the various verb forms (preocupada/o) v (preocupadarse). I hope that clears things up a bit, but I may have gotten in over my head trying to explain it.