Around that same time. Searching online I didn’t find anything saying it’s either one but rather both with both being acceptable (but not mixing as mentioned). Seems to depend on the teacher with lot of the older (possibly now retired) teachers being more familiar and teaching British English, sometimes as the only “correct” one and younger (not particularly young now) generation of teachers being more familiar with American English and teaching primarily that.
So, depends. Both are taught, there’s no unified policy for preference of one over another that I could find.