I found a really great website today to help with scanning. It's called For Better For Verse.
It is in a beta status right now, so I bet it will be really good when complete.
When you go there, you will see a particular poem (A Slumber Did My Spirit Seal). Ignore that for the time being. Click on overview. There is nothing really written there (part of being beta I guess), but you have tabs you can click on. Click on “Rules of Thumb” for some hints on how to scan poetry.
Then click on “Tools.” This is a must read if you intend to use this site. The only thing I would add to these instructions is so NOT add the foot mark at the end of the line—your answers will always be wrong.
From the tools page, you can get to the poems from a box on the right side of the page. There are various ways to sort the poems and for practice purposes, you might want to sort by difficulty level. Unfortunately, within a given level, they are just alphabetical even though each difficulty level has a pretty big range. The very easiest one is Rhyme for a Child Viewing a Naked Venus in a Painting of "The Judgment of Paris," which is hilarious without being risqué.
Beyond this one, I think most of us will get some wrong answers. But, one thing that is great about the site is that the “correct” answers are provided by a true expert and not some self-proclaimed Internet expert AND they sometimes provide for alternate acceptable answers. Plus, the “light bulb” notes that appear next to some lines after you submit your answers explain how deviation from the standard meter of the poem or line impacts the impression given by that line.
To use the site fully, you will need to know just a few terms: iamb, trochee, anapest, dactyl, spondee, pyrrhic (or really iambic, trochaic, anapestic, dactylic, spondaic, pyrrhic). But if you want to, you can copy and paste these definitions from here and print them out:
Iamb =unstressed, stressed
Trochee = stressed, unstressed
Anapest = unstressed, unstressed, stressed,
Dactyl = stressed, unstressed, unstressed
Spondee = stressed, stressed
Pyrrhic = unstressed, unstressed
The site also uses terms for the number of feet from monometer through hexameter, that is one foot through six feet, but these are in a drop down menu in order, so you don’t even have to memorize them.
Don’t let the fancy names put you off—it is a really, really cool interactive site. Also, don’t let wrong answers put you off. If you keep trying, you will get better (and don’t forget he rules of thumb, including the last one).