In the military organization of the later middle ages, a squire was a young man of good birth attendant upon a knight, frequently his own father. This excerpt concerning the training of a squire is originally from Ramon Lully (1235-1315), Le Libre del Orde de Caualyeria, translated and published in 1494 by William Caxton as The Book of the Order of Chivalry:

The knowledge and the school of chivalry is such that the knight makes his son to learn in his youth to ride, for it should take on the keeping of a horse. It behooves him also that he serve, and that he be the first subject of the lord, for otherwise he will not know the nobility of lordship when he should become a knight. And therefore every man who will come to knighthood should learn, in his youth, to carve at the table, to serve, to arm and to adoube a knight; for in likewise as a maid will learn to sew in order to be a tailor or a man to be a carpenter, it behooves them to have a master who can sew or hew. Likewise it behooves that a noble man who loves the order of chivalry and will be a knight to have first a master who is a knight, for thus it is a discovenable thing that a squire should learn the order and nobility from any other man than a knight. So very high and honored is the order of chivalry that a squire should suffer himself not only to learn to keep horse and learn to serve a knight, that he go with him to tourneys and battles; but it is necessary that he beholds the school of the order of knighthood. (from KCT Glossary, s.v. Squire)

For another medieval look at the training of a squire, see the poetic fragment written by John Harding (also from the KCT website).