Sometimes magazines are more willing to accept material on unusual themes than on more mundane ones. A poem about rainbows, for example, has to be pretty wonderful in order to get accepted for publication in a magazine. On the other hand, a poem written by a student about the dangers of smoking, drinking, or doing drugs, one that presents themes publishers might want to present, might stand a greater chance of being printed. Unless students know the topic about which they want to write, I ask them to brainstorm choices, and then we discuss which might make the best entry. Material one magazine would not publish may be perfectly acceptable to another.
Some magazines prefer to print poetry.
Others prefer stories. Short silly poems rarely win school-sponsored contests, but they do get published. If a student's poem is read to the class, and the class laughs heartily at it, this poem may be publishable in a magazine whose intended audience is that age. If a poem or story is rejected by a magazine, and the author believes in its quality, submit it to another. One of my students who loved to hunt wrote a beautiful story about the first buck he had shot.