I was the youngest Catholic there, and I don't recall learning about Purgatory in CCD growing up, but I was the one answering the questions and explaining the Church's teaching about purification after death.
Purgatory (a state of purging or cleansing or purification of the soul, after death, from the effects of sin) can be supposed from just a single verse of Scripture: "Nothing unclean shall enter it [the Heavenly Jerusalem]" (Revelation 21:27). Are we utterly clean now in life? (That is, are we utterly devoid of imperfection and sin?) If we are to enter Heaven, we must be utterly clean. So unless the very act of death cleanses us (which is supported by neither Scripture nor Tradition), there must be some sort of post-death cleansing of our souls.
The Roman Catechism (warning: big file) published following the Council of Trent, mentions it briefly (since the Catechism was meant as a guide to priests for instruction, rather than for the laity for learning) in the following ways:
... the fire of purgatory, in which the souls of just men are cleansed by a temporary punishment, in order to be admitted into their eternal country, into which nothing defiled entereth (cf. Rev. 21:27). The truth of this doctrine, founded, as holy Councils declare, on Scripture, and confirmed by Apostolic tradition, demands exposition from the pastor, all the more diligent and frequent, because we live in times when men endure not sound doctrine.The Baltimore Catechism describes the purpose of Purgatory in questions 184 (Lesson 14) and 424 (Lesson 31), quoting 1 Corinthians 3:13-15 both times:
Prayers for the dead, that they may be liberated from the fire of purgatory, are derived from Apostolic teaching.
We also beg of God ... that we be not sentenced to endure the fire of purgatory, from which we piously and devoutly implore that others may be liberated.
184. Who are punished in purgatory?The Catechism of Pope St. Pius X describes the purpose of Purgatory in question 118 on the Sacrament of Penance:
Those are punished for a time in purgatory who die in the state of grace but are guilty of venial sin, or have not fully satisfied for the temporal punishment due to their sins.
424. Where do we pay the debt of our temporal punishment?
We pay the debt of our temporal punishment either in this life or in purgatory.
118 Q. Do those who die after having received absolution but before they have fully satisfied the justice of God, go straight to Heaven?The modern Catechism of the Catholic Church (technically addressed to bishops) mentions Purgatory, but perhaps too briefly (1030-1032 and 1471-1479,1498).
A. No, they go to Purgatory there to satisfy the justice of God and be perfectly purified.
The Church has not forgotten about Purgatory, although many Catholics may have. I've compiled a few references from documents (Vatican II and later) that refer to Purgatory (whether by name or by the description of "purification after death"). The third one (Indulgentarium Doctrina) is an excellent source to help understand what the Church teaches about the effects of sin.
Vatican II, Dogmatic Constitution on the Church Lumen Gentium (1964), nn. 49, 51:
Until the Lord shall come in His majesty, and all the angels with Him and death being destroyed, all things are subject to Him, some of His disciples are exiles on earth, some having died are [being] purified, and others are in glory beholding "clearly God Himself triune and one, as He is"; but all in various ways and degrees are in communion in the same charity of God and neighbor and all sing the same hymn of glory to our God. ... This Sacred Council accepts with great devotion this venerable faith of our ancestors regarding this vital fellowship with our brethren who are in heavenly glory or who having died are still being purified; and it proposes again the decrees of the Second Council of Nicea, the Council of Florence and the Council of Trent.Pope Paul VI, Encyclical on the Holy Eucharist Mysterium Fidei (1965), n. 29:
Foreshadowed by Malachias, this new oblation of the New Testament has always been offered by the Church, in accordance with the teaching of Our Lord and the Apostles, "not only to atone for the sins and punishments and satisfactions of the living faithful and to appeal for their other needs, but also to help those who have died in Christ but have not yet been completely purified."Pope Paul VI, Apostolic Constitution on Indulgences Indulgentarium Doctrina (1967), nn. 3, 5:
That punishment or the vestiges of sin may remain to be expiated or cleansed and that they in fact frequently do even after the remission of guilt is clearly demonstrated by the doctrine on purgatory. In purgatory, in fact, the souls of those "who died in the charity of God and truly repentant, but before satisfying with worthy fruits of penance for sins committed and for omissions" are cleansed after death with purgatorial punishments. ... For this reason there certainly exists between the faithful who have already reached their heavenly home, those who are expiating their sins in purgatory and those who are still pilgrims on earth a perennial link of charity and an abundant exchange of all the goods by which, with the expiation of all the sins of the entire Mystical Body, divine justice is placated.Pope Paul VI, Apostolic Letter on the Credo of the People of God (1968), nn. 28, 30:
We believe in the life eternal. We believe that the souls of all those who die in the grace of Christ whether they must still be purified in purgatory, or whether from the moment they leave their bodies Jesus takes them to paradise as He did for the Good Thief are the People of God in the eternity beyond death, which will be finally conquered on the day of the Resurrection when these souls will be reunited with their bodies. ... We believe in the communion of all the faithful of Christ, those who are pilgrims on earth, the dead who are attaining their purification, and the blessed in heaven, all together forming one Church.Congregation for the Doctrine of the Faith, Letter to Bishops on Communion Communionis Notio (1992), n. 6:
In its invisible elements, this communion exists not only among the members of the pilgrim Church on earth, but also between these and all who, having passed from this world in the grace of the Lord, belong to the heavenly Church or will be incorporated into it after having been fully purified.Pope Benedict XVI, Encyclical on Christian Hope Spe Salvi (2007), nn. 45-48:
The early Church took up these concepts, and in the Western Church they gradually developed into the doctrine of Purgatory. We do not need to examine here the complex historical paths of this development; it is enough to ask what it actually means. ... Saint Paul, in his First Letter to the Corinthians, [writes]: “Now if any one builds on the foundation with gold, silver, precious stones, wood, hay, straw—each man's work will become manifest; for the Day will disclose it, because it will be revealed with fire, and the fire will test what sort of work each one has done. If the work which any man has built on the foundation survives, he will receive a reward. If any man's work is burned up, he will suffer loss, though he himself will be saved, but only as through fire” (1 Cor 3:12-15). ... Some recent theologians are of the opinion that the fire which both burns and saves is Christ himself, the Judge and Saviour. ... His gaze, the touch of his heart heals us through an undeniably painful transformation “as through fire”. But it is a blessed pain, in which the holy power of his love sears through us like a flame, enabling us to become totally ourselves and thus totally of God. ... [I]f “Purgatory” is simply purification through fire in the encounter with the Lord, Judge and Saviour, how can a third person intervene, even if he or she is particularly close to the other? When we ask such a question, we should recall that no man is an island, entire of itself. Our lives are involved with one another, through innumerable interactions they are linked together. ... So my prayer for another is not something extraneous to that person, something external, not even after death. In the interconnectedness of Being, my gratitude to the other—my prayer for him—can play a small part in his purification.I also refer you to Nicholas Hardesty's massive compendium of links and resources on Purgatory at Phat Catholic.