The ceiling effect

When educators or learning scientists introduce educational interventions into the classroom, they almost always observe a ceiling effect: The interventions have little to no effect on students who are already very good. This is consistent with what can observe in life in general. Those of us who are already good writers, math wizards, computer geeks, and so on can survive, even thrive, under the most hostile of educational circumstances.

The same is not true of weaker students. Students who have very little knowledge to start, have been educationally marginalized in some way, who have low spatial abilities or low working memory capacities--these are the students who are most badly affected by poor education and who can most greatly benefit from mentoriship and from well-designed instruction. Therefore, one prescription for educational interventions is to design and implement them for the people who need them most.