Sentence diagramming (also known as Reed-Kellogg diagramming) was a popular classroom grammar technique for nearly a century. It lost favor about thirty years ago, but several Surfnetkids readers recently suggested sentence diagramming as a topic. I hope this means grammar is making a comeback!
"Learning diagrams may look boring at first glance," explains the developer of this cool online app, but he suggests it worth the effort to "learn the magic." To start, simply type a sentence to diagram and press enter. Mouse over the words in the resulting diagram to view their part of speech. If the sentence can be parsed multiple ways, you'll see a small grey arrow in the upper right-hand corner. Click it to see the alternative diagram.
Eugene R. Moutoux's website is a treasure trove of diagramming goodness. Yes, it does include samples of sentence diagramming in German and Latin, but there is lots of English too! Start with the Basics (in two parts) then move on to goodies that include samples from literature and history. Have fun diagramming the preamble to the U.S. Constitution, the Gettysberg Address, or with really long opening sentences from half-a dozen classic novels. "There once lived, in a sequestered part of the country of Devonshire, one Mr. Godfrey Nickleby: a worthy gentleman, who, taking it into his head rather late in life that he must get married, and not being young enough or rich enough to aspire to the hand of a lady of fortune, had wedded an old flame out of mere attachment, who in her turn had taken him for the same reason." -- Nicholas Nickleby, by Charles Dickens.
There are four terrific sentence-diagramming tutorials here, but finding them is a challenge. . Here's some help. For a Powerpoint introduciton to sentence diagramming, click the blue graphic in the middle of the a yellow box, near the middle of the page. For a more in-depth tutorial (fifty pages long!) use the round blue Enter button, a half screen further down the page. Curious about how to diagram the Pledge of Allegiance or the Preamble to the U.S, Constitution? Look for those links below the Summaries subhead near the bottom of the page.
Learning stream explains sentence diagramming in seven steps. Step one? Look for the verb. "Ask the question, 'What action is taking place, or what happened in the sentence?' The answer you get will let you know which word (or group of words) serves as the verb in the sentence. The VERB is placed on the right hand side of the base line."
The user interface is bare bones, but just on through to Diagram Basics for a three-part overview of sentence diagramming. "To diagram a sentence, you have to divide it into its component parts, or constituents. The most important cut is between subject and predicate, which are separated with a vertical line. The predicate contains the verb marked for tense plus any objects or subjective or objective complements."