As I noted in an earlier post, when knights first appeared in the eleventh century, they were essentially henchmen on horseback. But during the eleventh and twelfth centuries, knighthood and nobility gradually fused, as each group wanted to be more like the other.
We know relatively little about how service knights were trained, but we do know quite a bit about the training of noble knights.
Little boys would be taught simple reading and arithmetic by their mothers, along with their sisters, but around the age of six or eight, they would be sent away for knighthood training. Generally boys were trained in groups, perhaps at the castle of their father's lord (say, a count), or perhaps with an uncle. Maternal uncles were preferred to paternal uncles, because a paternal uncle was at least a potential rival to one's father, whereas a maternal uncle was not.
Starting with ponies and wooden weapons, they would be trained to ride and to fight. They would learn to ride at an opponent while carrying a long lance, hoping to knock him off a horse; here they started by aiming a lance at a ring. They would grow accustomed to wearing armor, such as in the image above. This scene, from the abbey church of Vézelay, depicts the story of David and Goliath. David is cutting off the giant's head, and the giant, in long chain mail tunic and helmet with nose-piece, is wearing twelfth-century armor.
At the same time as they were learning to fight, boys would be educated, in reading, some writing, and some theology. They might practice writing love poems to the wife of the castle's lord. She probably enjoyed the attention of such adolescents, as long as they kept their proper distance.
(Click here for more on chivalry.)
By their late teens, the boys had finished their training. They would be formally "knighted" in an elaborate ceremony that involved a tournament and a party that might go on for days. Religious elements were introduced into the knighting ceremony, in a desperate and not altogether successful effort to suggest that being a knight was fundamentally about something other than killing people.
Young men were often knighted as a group, with comrades who would be their best friends for life. They were tough and superb fighters; even their enemies were agreed on that. In the twelfth century, when you really were not supposed to ride around killing people, a lot of new knights headed off on Crusade, or else followed the tournament circuit, while waiting for their fathers to die so they could inherit.
Click here for more on knights' horses.