I agree that the "they were never taught" fallacy is common among new teachers- as is the attempt to cover years worth of material in a few short weeks at the beginning the syllabus. I see this all the time with new teachers, and often have to insist that they are taking the wrong approach- students who can't add fractions aren't going to acquire it in two weeks.
Where I disagree is the idea that these student can't learn the material (they just can't catch up to the material in a few extra weeks of time)- I've known a few teachers whose students consistently perform better then their peer group, and retain the information into their next few courses. For one fifth grade teacher we tracked, by highschool his students were moving into advanced math courses at a much higher rate than students who passed through other fifth grade teachers at the same school. The value-added teacher research bares out the facts that good, experienced teachers can produce long-term learning gains in most of their students.
My suspicion is that many grade-school level teachers don't understand the material they teach (a surprising number of grade school teachers are essentially mathematically illiterate) and can inflict a fair amount of damage to student's understanding.
students who can't add fractions aren't going to acquire it in two weeks.
The original post seems to say that the students do acquire it in two weeks, they just forget as the class moves on to the next topic. Does that sound right to you?
Post by fellow LW reader Razib Khan, who many here probably know from the gnxp site or perhaps from his debate with Eliezer.