In many small communities, like St. Catharines, the Bar or Bat Mitzvah represented the end of the formal Jewish education of young people. However, after the dawn of the age of Jewish camping, and the resultant interest in continuing education for young people, it became obvious that young people also needed to continue on beyond the age of 12. It was an important way for Jewish education to continue to be strengthened, and bring Jewish teenagers together as friends and fellow students. Often, these Hebrew High Schools were started by a rabbi who had seen the success of such classes elsewhere.
In St. Catharines, the first Hebrew High School program was formed by Rabbi Dr. Israel Freedman and his wife Sheba. This was seen as so important that it was actually written into the contracts of newly hired rabbis that they would teach Hebrew High School Classes. Once the idea caught on though, like many other things, it became important for older people who had no opportunity to benefit from any formal Jewish Education while growing up, to want classes of their own. These classes would focus on the Prayer Book, Jewish History, Making a Jewish Home, and so forth, topics of interest of many adult learners.
In the first picture below, you see the first Hebrew High School graduating class of Rabbi Israel Freedman and his wife. That class met one night a week for three years, just like Hebrew School as we were growing up. The second picture shows a class which also met of an evening, but obviously the ages of the learners was far older. It is an old adage that you are never too old to learn new things.