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School Board Policy & Education Research
Write-in "Doug Mann" for School Board
by Doug Mann, 29 Oct 2004, Submitted to the Star-Tribune for publication 28 Oct 2004
Subj: School Board Policy & Education Research
Date: 11/20/2001 9:12:51 PM Central Standard Time
In a E-mail dated 11/19/2001 8:45:34 PM Central Standard Time, Michael Atherton noted:
"The variance proportions cited in the report were really 8%, 43%, and 49%,
not 8%, 42%, and 49% as cited in Ms. Johnson's post. And, if you know
anything about statistics and regression models then you should realize that
these proportions of variance are unrealistic. More on this to come."
Audrey Johnson's response:
"Whoops! Youv'e got me there Mr. Atherton! I am not a statistician, just a
liberal arts grad from the 70's and early 80's. Never was require to take
Audrey Johnson has been sitting on the Minneapolis school board for nearly two years now. The board claims to makes its policy decisions on the basis of research. Audrey Johnson also presents herself as something of an expert on educational research (as in her newspaper column). How can Ms. Johnson possibly evaluate that research without knowing something about statistics and regression models?
The report in question is entitled "Doing What matters Most: Investing in Quality Teaching," Prepared for the National Commission on Teaching and America’s Future, by Linda Darling-Hammond, Nov. 1997 <http://www.tc.columbia.edu/nctaf/publications/doing.html>
Referring to that report, Audrey Johnson said "...research shows that student achievement can be accurately measured as follows: 49% attributed to parent involvement and about 42% teacher quality, and about 8% to class size."
I can't open pdf files on my computer, so I didn't see the full report. However, an extract of the report by Linda Darling-Hammond that can be read on-line says:
" ...In combination, differences in teacher expertise and class sizes accounted for as much of the measured variance in achievement as did student and family background factors..."
The report says student and family background factors accounted for roughly half of the measured variance in academic achievement, not "parental involvement." The report also measures "teacher expertise," not "teacher quality."
In a E-mail dated November 11, I said:
"I expect the type of study to which Audrey Johnson refers would attribute at least 10 to 20% of test score variability to unknown or unmeasurable factors, some to household income, some to mobility (changing schools), and so forth. There may be a fairly high correlation between test score variability and parent involvement as it is measured by the Minneapolis Public Schools. But even a very strong statistical association between two factors does not necessarily mean that one factor is the cause of the other."
I'm sure that I've seen or heard of studies that attribute about 8% of test score variability to the difference between small (less than 17) and regular (about 25) class sizes. And 42% would be in the ball park for studies of teacher efficacy. However, teacher efficacy is typically measured as years of teaching experience, with adjustments for special training and certifications. If other factors that effect the quality of teaching are taken into account, they would be evaluated independently of teaching experience and qualifications."
In the extract from "What Matter Most" cited above, Linda Darling-Hammond says,
"In an analysis of 900 Texas school districts, Ronald Ferguson found that teachers’ expertise—as measured by scores on a licensing examination, master’s degrees, and experience—accounted for about 40% of the measured variance in students’ reading and mathematics achievement at grades 1 through 11, more than any other single factor. He also found that every additional dollar spent on more highly qualified teachers netted greater increases in student achievement than did less instructionally focused uses of school resources (see figure 4 in full report).
The effects were so strong, and the variations in teacher expertise so great that, after controlling for socioeconomic status, the large disparities in achievement between black and white students were almost entirely accounted for by differences in the qualifications of their teachers. An additional contribution to student achievement was made by lower pupil-teacher ratios in the elementary grades. In combination, differences in teacher expertise and class sizes accounted for as much of the measured variance in achievement as did student and family background factors."