The average cost of educating a child from kindergarten through high school graduation in Connecticut is about $165,000, up nearly 10 percent from last year.

According to Department of Education data, Hartford spent the most for each student who received a high school diploma, $283,482.

Colchester educated its students most efficiently of the 111 districts reviewed, spending only $129,099 over 13 years.

This measure of cost per graduate includes 13 years of per pupil costs divided by the graduation rate to adjust for students who the district paid to teach but who did not graduate.

New Britain, New Haven, Windham and New London are the next most expensive school districts.

The Glastonbury, Tolland, Wolcott and Suffield school districts joined Colchester as the most efficient in the state. They accomplished this by combining relatively low total costs per student and high graduation rates.

Madison ranked as seventh-most efficient school district, yet it has the highest average performance on the Connecticut Academic Performance Test.

Especially in wealthy districts, spending and test results don’t have a clear relationship. In a number of the comparison groups established by the state, more efficient districts have test results that are indistinguishable from their peers.

Ridgefield has similar outcomes to Westport, yet spent $40,000 less on the career of each student. Glastonbury outperforms Greenwich on the CAPT, yet spent $70,000 less on each student.

Raising Hale has done similar rankings in 2010, 2011 and 2012.

The Department of Education changed the way it calculates graduation rates two years ago. Since there is a two-year lag in the data, this change is reflected for the first time in 2012.

Under the new method of calculating graduation rates – by cohort, or incoming freshman class – many graduation rates are lower than under the old method.

The change in methodology makes it difficult to compare 2011 and 2012 data. However, the data for 2012 and 2013 are comparable.

2013 Data

Sorted by Rank | DRG| Alphabetical

Highest-cost districts
1. Hartford School District $283,482
2. New Britain School District $274,361
3. New Haven School District $267,897
4. Windham School District $258,565
5. New London School District $255,988
Average cost: $164,672
Lowest-cost districts
107. Glastonbury School District $131,679
108. Tolland School District $130,311
109. Wolcott School District $129,254
110. Suffield School District $129,178
111. Colchester School District $129,099

Methodology:

To calculate the cost per graduate, the Yankee Institute took data from the Connecticut Department of Education for average annual expenditures per student going back 13 years, representing kindergarten through 12th grade. After totaling the cost, it was divided by the graduation rate to come up with the lifetime cost per graduate. The 13th year is the 2010-2011 school year, and data is not adjusted for inflation, so the real cost of 2012 graduates is higher than calculated. Communities with high annual costs, more drop outs and lower graduation rates end up with the more expensive graduates. Some regional school districts, districts with less than 13 years of data, charter schools and other non-traditional schools were left out of the calculations to keep the data consistent for the greatest number of schools.

Also, the calculations do not include costs for school construction or teacher pensions, both of which are paid for by the state.

Correction: A correction to the 2012 report has resulted in updated “change in adjusted rank” for many school districts. New London, New Milford and Newington has additional comparison changes.

Yankee Institute intern Sam Teixeira contributed to this article. He is a junior studying political science at the University of Virginia. He lives in Norwich.