You can read the story here, and you should. Basically, St. Paul's was created by a 1919 split in an older congregation, Rockway Lutheran. The split was occasioned by tension between two models of church polity. Rockway's Sunday School director felt that the Sunday School ought to be not merely lay-led, but wholly independent of the pastor's authority. The pastor felt otherwise.
Yes, we all know that Sunday School was originally a lay movement, which sometimes took on an anticlerical tone. But in the story by Tom Stafford, which is drawn principally from a 1989 historical paper by a former pastor, we see the movement in a transitional phase. The Rockway Sunday School was, at least officially, an organ of its congregation. And yet since 1890 -- that is, for thirty years -- it had insisted upon administration independent of pastor and vestry. It was, in other words, an independent entity, sharing facilities and members with the congregation.
Clearly, this was not the position that would eventually prevail. Within a few decades, "Sunday School" had come to be thought of as one of the most basic ministries of a parish, but clearly one belonging to the parish, and for which the parish's usual leaders had ultimate responsibility. Although we have seen several power-struggles waged between congregation councils and their parochial or preschools, often where substantial sums of money were involved, we have a hard time even placing Sunday School into the same category. It has long since become something quite different than it was.
Parenthetically, we note this slightly-funny bit: as late as World War I, these German-Americans could still publicize their church organizations as, for example, "the Rockway S.S." You wouldn't see that a few years later.
And this one: The split may have been an accident. After an especially difficult congregational meeting, one participant got up to go to work. His departure was apparently misinterpreted as a "walk-out." (Would history be different if everybody had realized that a bunch of professor at Concordia, St. Louis, were just late for class?)