You said you don't distinguish between infallible doctrine and dogma but are all doctrines infallible? 
I guess I was surprised by the one teacher as I think science should be taught by science teachers etc. Did you mean moral, or religious teaching not all other teaching? 
About things like slavery and usury-do you not define those as doctrines and therefore change in them is acceptable? 
I'm in the US, a former primary teacher, way over 70! And most of my religious training after childhood came from various courses I've taken in church history-shocked to find all seven sacraments were not defined as dogma/ doctrine untill Trent! and sacraments including the history thereof, some spirituality-though much of that was too non logical/literal for me!, Never thought before this about what Jesus probably thought of the word priest. Had a hard time studying scripture as I'm very literal and the Jews were not Greeks! In other words they used metaphorical language which floored me for years!