So about the title, ups and downs. Yesterday in 5th grade I had a major flop of a lesson. Ok, here is the gist, I tried following the textbook, (mistake) and the lesson was on front-end estimation with adjustment. This isn't even really a standard that I need to teach, just for the mathematical practices. The students were ok with addition, but when we hit subtraction all I could tell them was do it this way because I said so! I couldn't for the life of me explain it without saying, this is the way you do it, so do it! Does that make sense? The textbook, which for the most part, I really love even said "Make a poster showing the two ways to use front-end estimation with adjustment for subtraction so that students remember." Not how to explain why it works, just have them memorize! UGH!
Here are the examples I used to teach them, which come straight from the book.