Ok, so I looked around and and found this on wikipedia... http://en.wikipedia.org/wiki/Whipping_boy

I was wondering if there were any other occasions this went on, specifically if it ever happened earlier then the 15th century. Also if there were any period sources I could look into about this.

I am teaching two boys at the ages of 11 and 12th and the book they were reading brought up the question as to how common this was. If Knights ever did this to their sons or if it was only on a royalty bases.

Thanks for any help in this quarry.

I have no specific knowledge on whipping boys, only general knowledge on medieval monarchy, but I would be surprised if this went on with other people than sons of kings. This looks to me (as the article also analyses it) like one of the many ways the king was sacralized and set apart from the mere mortals he ruled, to express the fact that he was "God's lieutenant on Earth" and thus sacred.

This could have appeared before the 15th c. in highly ceremonialised courts (such as the German emperors', who at times deployed an extensive propaganda to show how special they were) but it is certainly a fact that the rise of the kings' power and the first elements of absolutism, especially in the 16th c., brought about many complex ceremonial novelties that were meant to further the monarchy's prestige. So the period indicated on Wikipedia for the creation of the whipping boys is pretty coherent with the general tendencies in the history of the monarchic instution.

Other than these general elements I know nothing, so do try to find a better source :p

I've seen an academic article on the subject, which you can read online.

Mark H. Lawhorn, "Taking Pains for the Prince: Age, Patronage and Penal Surrogacy in Samuel Rowley's When You See Me, You Know Me," in The Premodern Teenager, ed. Konrad Eisenbichler (Toronto: CRRS Publications, 2002), pp. 131-150.

It discusses the matter in a roundabout way, by looking at an Elizabethan play about the young Edward VI and his whipping boy. The real Prince Edward's whipping boy was apparently the son of a rebel Irish chieftain. He had been sent to be fostered at the royal court as an unofficial hostage for his father. (See p. 141.)