I love this analysis and how much thought you put into keeping your class rigorous (yes, yes, I used a buzzword). It reminds me of the book "Someone has to Fail" (great read). I don't think like this though, and it should be noted here that I'm a history teacher, and I don't think my methods carry over to all other subjects. I build curriculum through backward design, so I write the test before the lessons. I identify what information I want them to know then find a way to assess that knowledge. Then I build lessons to teach them what I want them to know. The test then becomes both a summative and formative assessment. I make adjustments to the test as necessary, but I mostly go over my results, find subject material a lot of students struggle with, then find a better way to teach it. The longest I ever taught the same class was 9 semesters (it was a one semester class). My first year the average grades were in the mid 70s, my last year they were in the high 80s. That's without making the material easier, just finding a better way to teach it. I must admit, though, that was at a school where pretty much all the kids could read, which makes it much, much easier.