TOO MUCH, TOO SOON!
It really bothers me that some teachers jump in to teaching the formal algorithms way too soon. Last year, I was in a year 2 classroom where the teacher was trying to use the subtraction algorithm to work out elapsed time. It simply did not work and the kids had no idea what they were doing! The saddest part was that I asked the teacher if I could chat with the kids after the lesson was completed, and it turned out most of them were able to solve the problem mentally, just by working backwards. When we teach the algorithms, they stop using those mental strategies that are far more efficient! There is also no mention in our curriculum of introducing the algorithms to year 2 students. (Australia)