Teenagers are certainly appropriate for the sophistication of Dramatica stories especially when you consider how many pre-teens have devoured the Harry Potter novels. Don't sell them short.
Dramatica can be used for grade school stories if you treat them like short stories (limited breadth) OR limit the depth of the story's exploration. You won't need many of the tools in the Dramatica software, but the StoryGuide Level 1 covers most of the children's story elements you need.
The biggest difference between children's stories and grand argument (Dramatica) stories is in the storytelling. You can tell a grand argument story simply and in simple language. However, some writer's prefer simple tales ("This happened, then this happened, then this happened, and this is where it all ended up.") to stories ("With things set up this way, this is how everything went and the naturally leads to this one and only conclusion.").
The biggest difference between tales and stories is how their "message" is created. In a tale, the meaning of the story comes from comparing the starting point with the ending point. Change either the starting point or ending point and the message changes. In a (grand argument) story, the meaning is built into every piece of the story. Leave a piece out and the story still has the same meaning (though a "hole" might be noticed). A tale makes a statement: This leads to that. A story makes an argument: When these things come together they naturally come to this inevitable conclusion.