Asher Asa Lecha Amalek BaDerech Betzetchem MiMitzrayim"
On the Shabbat that precedes Purim, two Torah scrolls are taken from the ark; one for the regular parsha and one for the Maftir - 'Remember what Amalek did to you' (Dvarim 25). Because of this reading, it is called, Shabbat Zachor (Remember). The Haftorah also deals with Amalek.
There is a mitzvah in the Torah to remember Amalek and his descendants and to orally recall their iniquity. We are to tell our children in each generation what the people of Amalek did to us during our departure from Egypt. This mitzvah will be fulfilled completely only when we shall have caused Amalek's memory to perish, and their name to be erased from the world, together with the slightest remnant of anything that bears their name. As the Torah says: 'Remember what Amalek did to you on the way, upon your departure from Egypt'... 'You shall erase the memory of Amalek from beneath the heavens, you shall not forget.' Upon which the Sages have expounded: 'Remember,' orally - 'You shall not forget,' in your heart.
To properly fulfill this commandment, the Sages have prescribed the public reading of this passage from a Torah scroll, once every year, on the Shabbat which precedes Purim - so that the 'wiping-out' of Amalek might be adjacent to the 'wiping-out' of Haman, the latter being a descendant of Amalek.
Although this passage is read yearly in the parsha of Ki Tetzeh (which we read towards the end of the summer), we still must read this passage separately in its prescribed time before Purim. This is done in fulfillment of the Torah's commandment to remember the cowardly attack of Amalek.
Some authorities say that if one fails to hear Parshat Zachor, he fulfills his obligation through hearing the prescribed Torah reading on Purim: ('And Amalek came').
A boy who is not yet of Bar-Mitzvah age should not be called to the Torah for Maftir on Parshat Zachor. Nor should he read the parshah for others. For since he is free of the obligation of mitzvot, he cannot enable others to fulfill their obligation through him.