Do you have a ministry in your parish? I vividly recall during freshmen week in college the campus chaplaincy would advertise the various "ministries" available to students: reading, Eucharistic ministering, making sick visits, "singing", usher jobs, and hospitality. To the priest were reserved the words "This is my body", "I baptize you", and "I absolve you"; otherwise, it was open season on liturgical roles in this protracted state of infancy.
What if I told you that there were ways that the faithful informed the practice of the Latin liturgy without clericalizing themselves and laicizing the clerics? What if I told you that England was once an exemplar of participatio actuosa in the Mass? What if I told you that the priest's private devotion at the end of Mass was also, in many cases, the congregation's public devotion?
The medieval Roman liturgy and its local variations almost always concluded with the so-called Last Gospel, the first fourteen verses of the Johannine prologue. A 1474 printing of the Roman Missal in my possession makes no mention of it. The Dominicans did not add it until after Trent. And the last public words in the Sarum Mass were In nomine Patris et Filii et Spiritu Sancti. Amen. Yet, the Last Gospel was near ubiquitous as a private devotion before the Council of Trent. The celebrant would recite In principio erat Verbum until plenum gratiae et veritatis quietly on his way back to the vestry. The neo-Gallican rites retained this for high Mass, although they generally followed the Tridentine arrangement of low Mass. The Roman rite continued the medieval custom for Pontifical Mass and Quintin Montgomery-Wright retained it at Le Chamblac. So, how was the clerical devotion an act of lay participation?
Prior to modern printing people did not "know the Bible", but through sermons, catechesis (as far as it was available outside cathedral cities), stained glass, and mystery plays commoners could certainly be expected to know the main stories from the Old and New Testaments that the Scriptures record. The faithful often asked for particular passages to be read at the end of Masses celebrated for their specific intentions, believing that, aside from any instructional value, the readings contained a latria efficacious as prayer to God, that the readings were an act of worship themselves if done for the proper purpose.
Where do these readings appear in the Missals of the day? No where at all. They were recited at private Masses before the Johannine In principio, not in place of it. Benefactors, with the consultation of the celebrant, could select votive orations for the commemorations at the Masses they endowed, but did not alter the structure of the Mass. Instead, they had their own liturgical devotion along with the celebrant, one that they believed "especially powerful, to bring particular blessings or protection from certain evils.... Even the unlettered laity noticed, and valued such variations" (Duffy).
In those days before the 40 hour work week attendance at weekday Masses for special intentions was normal. A private Mass was not a Mass said in a private place, but rather any Mass that was not the canonical norm for the community; cathedrals, monasteries, and collegiate churches had to celebrate the Mass of the day every day, while a parish needed only celebrate the Mass of the day for feasts and Sundays. Anything beyond that—from a Marian votive Mass to an anniversary Requiem—could reasonably be called a "private Mass" and the prayers within it subject to the needs of those who asked for it (KL Wood-Legh).
The "people" valued the readings as both instructions and as a form of prayer for their own needs and so added them to the liturgy, albeit not the public liturgy, of the Church in their time. Whether or not they comprehended every word, they understood the general thrust of what was happening and valued it, knowing they did their duties as providers for their caring parsons and monks, who offered their desired votives. It is rather like the act of baking the prosphora for the Divine Liturgy.
Could there be a more grounded example of participatio actuosa? I may go down to a local parish and ask for Gospel passage of the crowd demanding Our Lord's death when I next commission a Mass for the conversion of those who worship at the Galleria shopping mall.