Objection 1. It would seem that Christ learned something from man. For it is written (Luke 2:46-47) that, "They found Him in the temple in the midst of the doctors, hearing them, and asking them questions." But to ask questions and to reply pertains to a learner. Therefore Christ learned something from man.
Objection 2. Further, to acquire knowledge from a man's teaching seems more noble than to acquire it from sensible things, since in the soul of the man who teaches the intelligible species are in act; but in sensible things the intelligible species are only in potentiality. Now Christ received empiric knowledge from sensible things, as stated above (Article 2). Much more, therefore, could He receive knowledge by learning from men.
Objection 3. Further, by empiric knowledge Christ did not know everything from the beginning, but advanced in it, as was said above (Article 2). But anyone hearing words which mean something, may learn something he does not know. Therefore Christ could learn from men something He did not know by this knowledge.
On the contrary, It is written (Psalm 45:4): "Behold, I have given Him for a witness to the people, for a leader and a master to the Gentiles." Now a master is not taught, but teaches. Therefore Christ did not receive any knowledge by the teaching of any man.
I answer that, In every genus that which is the first mover is not moved according to the same species of movement; just as the first alterative is not itself altered. Now Christ is established by God the Head of the Church--yea, of all men, as was said above (Question 8, Article 3), so that not only all might receive grace through Him, but that all might receive the doctrine of Truth from Him. Hence He Himself says (John 18:37): "For this was I born, and for this came I into the world; that I should give testimony to the truth." And thus it did not befit His dignity that He should be taught by any man.
Reply to Objection 1. As Origen says (Hom. xix in Luc.): "Our Lord asked questions not in order to learn anything, but in order to teach by questioning. For from the same well of knowledge came the question and the wise reply." Hence the Gospel goes on to say that "all that heard Him were astonished at His wisdom and His answers."
Reply to Objection 2. Whoever learns from man does not receive knowledge immediately from the intelligible species which are in his mind, but through sensible words, which are signs of intelligible concepts. Now as words formed by a man are signs of his intellectual knowledge; so are creatures, formed by God, signs of His wisdom. Hence it is written (Sirach 1:10) that God "poured" wisdom "out upon all His works." Hence, just as it is better to be taught by God than by man, so it is better to receive our knowledge from sensible creatures and not by man's teaching.
Reply to Objection 3. Jesus advanced in empiric knowledge, as in age, as stated above (Article 2). Now as a fitting age is required for a man to acquire knowledge by discovery, so also that he may acquire it by being taught. But our Lord did nothing unbecoming to His age; and hence He did not give ear to hearing the lessons of doctrine until such time as He was able to have reached that grade of knowledge by way of experience. Hence Gregory says (Sup. Ezech. Lib. i, Hom. ii): "In the twelfth year of His age He deigned to question men on earth, since in the course of reason, the word of doctrine is not vouchsafed before the age of perfection."
Source: Summa Theologica (New Advent)