Don Bosco, before Garelli?

In the Salesian tradition, there is a great narrative spun around the first interaction of Don Bosco with Bartolomeo Garelli, the boy whom Don Bosco meets in the church of St Francis de Sales.  This encounter is signposted as the origin of the Salesian oratory and the work of Don Bosco for the poor and marginalised youth.

However, it is not widely known that Don Bosco was already working for a section of the boys whom he would dedicate his life to, much before he met Bartholomeo Garelli.  Fr Cafasso, his spiritual director and guide, used to teach catechism every Sunday to bricklayers' boys.  And when he could not do it any longer, Don Bosco did it and he began with two boys. Not sure if he was requested to by Cafasso, or he took it upon himself, of his own accord.  Would be interesting to actually locate this in the historical chronology.  If so, then that Sunday catechism, rather than the Garelli encounter, could very well be the foundation of Salesian work.  Nonetheless, this historical evidence (as found in the Salesian Sources, Vol. 1) aids in understanding better the ambience in which Don Bosco found himself at home with - boys from the disadvantaged background.