If you don't have low ratios and tracking, you end up targeting the 33rd percentile and seeing: * Where the lower-third of the class gets with instruction with

If you don't have low ratios and tracking, you end up targeting the 33rd percentile and seeing: * Where the lower-third of the class gets with instruction with slightly too difficult material and not quite enough coaching. * Where the middle-third gets with excessive coaching on slightly too easy material. * Where the upper-third gets on their own with little help, occasionally bored by and impeded by the path of the overall class. This is somewhere affluence matters-- if you have parent volunteers showing up and hanging out to intensively coach (under the teacher's direction) the lowest readers and to challenge / help higher readers pick out books... it makes a big difference on how well class time is used. The teacher can aim square for the middle. And the stronger kids get some enrichment and opportunity for further growth. Why the 33rd percentile? Because a classroom with 1/6th of kids not getting it at all and 1/6th kind-of getting it.. is infinitely more workable than a classroom with 1/4th not getting it at all and 1/4th kind-of getting it.