Two brothers agree to wrestle on their way to school. In the process, one is wounded by the other's knife. The unwounded brother (often) tries to save the wounded one, but it is too late; all that is left is to arrange for his burial and make excuses
In Friedman's A version, the brother is killed, not wrestling for fun, but in a fit of passion. - PJS
Indeed, this motif (which is not unusual; many of Davis's texts have it, for instance) gives rise to the possibility that what we have here is two songs mixed. Call them "The Twa Brothers" and "The Rolling of the Stones." In the former, the one brother kills the other as a result of accident or perhaps a (step?)mother's malice."
"The Rolling of the Stones," though it involves a death and is usually listed as a version of this song, has a very different feel. It is definitely a song of passion and jealousy, and ends with Susie, the girl of the piece, dancing to try to bring the dead man back to life.
The two have certainly mixed verses, making them hard to tell apart, but I'm not at all convinced that they are the same song. A curiosity is that the "Rolling of the Stones" texts seem to be mostly American, even though American texts rarely involve magic. But it should be noted that the endings of the texts in Child are very diverse; it may be that he simply hadn't found one of the "magic" endings.
Linscott has one of her usual folklorish explanations: "The event from which the ballad gets its theme happened near Edinburgh in 1589, when one of the Somervilles was killed by the accidental discharge of his bother's pistol." This connection ignores the fact that brothers are more than a little apt to quarrel over inheritances....
E. K. Chambers (_English Literature at the Close of the Middle Ages_, p. 72) quotes a passage from a thirteenth(?) century fragment of a song which has not been connected with this piece, but which I find rather interesting:
Atte wrestling my lemman I ches,
And atte ston-kasting I him for-les.
At wrestling my love I chose,
And at stone-casting I him lost. - RBW
Also collected and sung by Ellen Mitchell, "Twa Brithers" (on Kevin and Ellen Mitchell, "Have a Drop Mair," Musical Tradition Records MTCD315-6 CD (2001)) - BS