Monday, June 16, 2008

UK Education officials stuggle to explain attainment versus growth

Educators and policymakers in the US are not the only folks to struggle with explaining what can appear to be contradictory outcome measures. A recent report identifying failing schools described a wide range of growth performance. In particular, this story points to 30 schools who were in the top 5% on attainment measures (number of GCSEs) but failing on growth.

This is something many people have trouble discussing. The notion of "controlling" for prior ability and demographic characteristics gets confused with expectations. What controls do is level the playing field by making a fair comparison. From a social policy point of view, positive or negative coefficients on for gender, economic status, or race have nothing to do with expectations. They are are the growth equivalents of attainment gaps. If economically disadvantaged children in the 5th grade show on average that their growth in test scale score is 4 points lower than non-poor students, this is the performance gap. This tells us how well we are doing helping students overcome the educational impact of the non-school economic resources. Policy should be focused on improving the rate of learning growth to erase the growth gap.

The challenge presented by interpreting high attainment versus low growth is actually not that hard to overcome. We all know of schools that are good at recruiting families and students with high prior test scores. Many adds for new homes included references to the attainment levels of local schools. High prior school-level attainment (and school magnate programs) tends to attract families with high attainment students. Recruiting students with high prior attainment is the simplest way to be a high performance school under an accountability system that focuses on attainment. A growth model, instead, controls for prior attainment and teases out what learning was delivered in that year. A school can be very good at recruiting while being not very good at challenging good students. The two things are quite different.


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