From the various schools directed by the church pupils with good voices were selected for training in the Schola Cantorum. They became inmates of the dormitories of the Pontifical establishment and pensionaires, except in the cases of children of noble birth, who received no pensions. All were educated in the several liberal arts. They were under the immediate direction of the masters of chant, called paraphonists. These were four in number, named, in order of rank, primicier, secundicier, and so forward. In due course the title of paraphonist was conferred on the most skilful of the pupils, such as were competent to sing the solos of the “alleluia.”

The period devoted to the studies of the Schola Cantorum was nine years. The instruction was both theoretical and practical, but the length of the time of study was demanded chiefly by the requirement that all the chants should be memorized. Only the director or the soloist was permitted to have a book. In the classes the teacher was seated at the monochord, from which the pitch was communicated to the students.

All the singers, boys as well as men, had their heads shaved and wore chasubles. In the procession the singers marched in two ranks, the instructors outside, the boys inside, and in the chancel they retained this order. The choirs were small. They were generally in groups of about twenty or thirty soloists. The ensembles of the service were sung by the choir, the clergy and the congregation, but the most important parts were reserved for the trained vocalists. It is not difficult to present to the imagination the character of the singing of these artists, selected with scrupulous care and rigorously trained. The voices must have possessed the power and flexibility which we have long associated with the best Italian singing. Something of the ancient style is preserved in the present choral body of the Sistine Chapel and certain other churches in Rome. The visit of the so-called Vatican Choirs to the United States in the autumn of 1919 gave many music lovers opportunity to hear the masterpieces of the later church composers sung by a choir of this kind, but of pure Gregorian music nothing was offered.

[…]

What we learn from the monuments of these early centuries it that singing demanded first of all a command of long flowing phrases, the fundamental requisite of a vocal art similar to that demanded by the classic operas of the Handelian era. It is evident that a perfect legato was the base of all singing for not less than eighteen centuries, and that violent attack, forcing of tone, and the clarion delivery of high notes came to be popularly desired in the early part of the nineteenth century.

Henderson, William James. Early history of singing. New York: Longmans, Green, 1921.