The custom of Kabbalat Shabbat as part of the public prayer service is relatively recent.
It originated with the sages of Kabbalah in Safed, in the second half of the seventeenth century C.E.
Because it comes from a single source and began not too many generations ago, it is essentially uniform.
Moreover, because Kabbalat Shabbat comprises only Psalms and Piyyutim (liturgical poems not part of the ordinary order prayers) in some congregations boys under Bar Mitzvah age are allowed to be the cantors for this prayer.
Kabbalat Shabbat is made up of six psalms: Psalms 95 through 99 and Psalm 29, recited with elevated spirit and joyful enthusiasm (in some places, the recitation of these psalms was accompanied by musical instruments; however, halakhic authorities ruled to abolish this custom).
According to some sources, each of these six psalms corresponds to one of the weekdays and is intended to elevate it to a state of completion and perfection; it was also pointed out that the numerical value of the first letters of these six psalms is equal to the numerical value of the Hebrew word nefesh, "soul," alluding to the "additional soul" of Shabbat.
–Rabbi Adin Steinsaltz
From A Guide to Jewish Prayer, p. 108, by Rabbi Adin Steinsaltz