or sigma, in achievement scores better
than the standard lecture-based class,
and the individual tutoring gives you 2 sigma
improvement in performance.
To understand what that means,
let's look at the lecture-based classroom,
and let's pick the median performance as a threshold.
So in a lecture-based class,
half the students are above that level and half are below.
In the individual tutoring instruction,
98 percent of the students are going to be above that threshold.
Imagine if we could teach so that 98 percent of our students
would be above average.
Hence, the 2 sigma problem.
Because we cannot afford, as a society,
to provide every student with an individual human tutor.
But maybe we can afford to provide each student
with a computer or a smartphone.
So the question is, how can we use technology
to push from the left side of the graph, from the blue curve,
to the right side with the green curve?