The verb “kneel” has two past-tense forms: “kneeled” and “knelt.” “Kneeled” will probably win in the end. Here’s why.
Joshua asked, "Is there *really* no difference between "kneeled" and "knelt"? I want to say that "knelt" is more British, but I can't find anything to back that up. Are there really just two words with the same definition that you can use interchangeably depending on which you think looks or sounds nicer?"
Yes, it appears the two words are interchangeable. A small number of verbs are currently making the transition from irregular verb to regular verb and have two coexisting past-tense forms. Sometimes the distinction is British versus American because the British held on to the irregular form more strongly than we Americans did. The verb "dream" is one example: "dreamt" is considered more British, and "dreamed" is considered more American.
Irregular verbs tend to become regular over time. For example, "chide" (meaning something similar to "to scold") is a verb whose past tense shifted to the regular form relatively recently. The past tense used to be "chid," but now we're more likely to say "chided," as you can see in this Google Ngram search result.
Sometimes the distinction between two past-tense forms is a matter of where you live—London or New York—but sometimes the two forms exist simply because a word is transitioning, which seems to be the case with "kneel." A Google Ngram search shows that "knelt" is still more common in both British and American English. Eventually, everyone will probably forget about the irregular form ("knelt"), and the past tense of "kneel" will simply become "kneeled" because that's the most common direction of language change: to the regular form. Until then, you can use whichever one sounds better to you.
Mignon Fogarty is Grammar Girl and the founder of Quick and Dirty Tips. Check out her New York Times best-seller, “Grammar Girl’s Quick and Dirty Tips for Better Writing.”