Stoichiometry, "the quantitative relationship between two or more substances especially in processes involving physical or chemical change" (Merriam-Webster), is currently a major part of the U.S. high school curriculum. Given a balanced chemical equation, a student must be able to convert the quantity (in moles, atoms/molecules/formula units, mass, or volume) of one substance into the quantity of another substance and/or another kind of quantity in the equation.
However, I was not taught this in my own high school chemistry class, about 47 years ago. Others near my age also were not taught this. So when did this subject begin to be a common part of high school chemistry?
Note that I am not asking when the concept or the term was invented (by Jeremias Benjamin Richter: see this link or this one), just when it was commonly taught in American high schools. My web searches can find many pages on doing or teaching stoichiometry or on its origins, but nothing on the history of its teaching.