Statewide programs in Florida, Louisiana, and Ohio, however, already have demonstrated clear
positive effects on the
achievement of
students who remain in public schools, confirming Caroline Hoxby's claim (see «Rising Tide,» features, Winter 2001) that competition from choice
generates «a rising tide that lifts all boats.»
If teachers tend to rely more
on lectures when assigned more capable or attentive
students, this would
generate a
positive relationship between the amount of time spent lecturing and
student achievement, even in the absence of a true causal
effect.