Diagramming sentences is a visual way to show how the words in a sentence are related to each other.
The fun thing about interjections is that they are actually not grammatically related to the rest of the sentence, and diagrams of interjections make that easy to see.
To diagram an interjection, you simply float it on a line hovering above the rest of the sentence.
Interjections sit on a line above the subject of the sentence, and they are not joined to any other part of the sentence.
That's a pretty good way of showing that they aren't related to any of the other words, isn't it?
Here is an example for you to check out:
Your site gives English learners and teachers a great idea for learning English. Grammar is important to language learning, and your diagramming method makes language learning simpler and easier.