1. Measuring Student Growth
An introduction to
Value-Added
SCRIPT
This is a presentation adapted from one created by the Value Added Resource Center out of the University of Wisconsin to reflect Florida elements.
The purpose of the presentation is to introduce the concept of using a Value-Added model to measure student growth and to compare it to other methods of measuring student performance.
We are going to do this by using an analogy of gardeners working hard to grow oak trees. Think about how this relates to teachers helping students learn.

2. How do we measure student performance?
What do we want to do?
Evaluate based on student testing performance
Student outcomes determine whether the school is performing well
Evaluate schools for meeting the needs of all students
Accept students wherever they start and help students learn as much as possible from that starting point
Hold schools accountable for what they can control
Do not reward or penalize schools based on aspects of student performance they do not control
Measure should be valid regardless of differences in student population
Start by thinking about student achievement growth as it relates to measuring teacher effectiveness.
If our goal is to determine the effectiveness of teachers and schools based on student achievement growth, what do we want to do?
We want to evaluate based on student testing performance on the assumption that student outcomes determine whether the teacher or school is performing well.
We want to evaluate whether we are meeting the needs of all students and helping them grow on the assumption that teachers and schools should take students wherever they are when you get them and help them learn as much as possible from that starting point.
We want to hold schools accountable for what they can control.
We should not reward or penalize schools based on aspects of student performance they do not control.
Our measure should be valid regardless of differences in student population.

3. How do we measure student performance?
How do we do this?
Attainment (example: the current NCLB method… percent proficient)
Gain / Growth (example: Florida’s FCAT Learning Gains)
Value-Added (example: Florida’s Value-Added Model)
The following non-education example tries to illustrate the difference between these measures.
Three different ways of measuring student performance include attainment, gain or growth, and Value-Added.
NCLB/AYP is an example of measuring by attainment.
FCAT learning gains are an example of measuring gain or growth based on where students were and how much an achievement level or DSS score improved over a year.
Florida’s value-added system is one version of a value added model.
The following non-education analogy, the Oak Tree Analogy, illustrates the difference between these measures.
Conclusions about growth can be based on the same data, but the information each of these different growth models tells us can be very different.

4. The Oak Tree Analogy
This Oak Tree Analogy should help you better understand the basic concepts of value added, whether applied to trees or students.

5. Explaining the concept of Value-Added
by evaluating the performance of two gardeners
For the past year, these gardeners have been tending to their oak trees trying to maximize the height of the trees.
Each gardener used a variety of strategies to help their own tree grow… which of these two gardeners was more successful with their strategies?
In this analogy, we will be explaining the concept of Value-Added by evaluating the performance of two gardeners.
For the past year, these gardeners have been tending to their oak trees trying to maximize the height of the trees.
Each gardener used a variety of strategies to help their own tree grow.
We want to evaluate which of these two gardeners was more successful with their strategies to make their tree grow.

6. To measure the performance of the gardeners, we will measure
the height of the trees today (1 year after they began tending to the trees).
Using this method, Gardener B is the superior gardener.
This method is analogous to using an Attainment Model.
To measure the performance of the gardeners, we could measure the height of the trees today, 1 year after they began tending to the trees.
With a height of 61 inches for Oak Tree A and 72 inches for Oak Tree B, we find Gardener B to be the superior gardener.
This method is an example of using an Attainment Model to evaluate performance.

7. … but this attainment result does not tell the whole story.
Oak A
Age 3
(1 year ago)
Oak B
These trees are 4 years old.
We need to find the starting height for each tree in order to more fairly evaluate each gardener’s performance during the past year.
The trees were much shorter last year.
…but this attainment result does not tell the whole story.
These gardeners did not start with acorns. The trees are 4 years old at this point in time.
We need to find the starting height for each tree at the beginning of the year in order to more fairly evaluate each gardener’s performance during the past year.
Looking back at our yearly record, we can see that the trees were much shorter last year.
Oak A
Age 4
(Today)
Oak B

8. This is analogous to a Simple Growth Model, also called Gain.
We can compare the height of the trees one year ago to the height today.
By finding the difference between these heights, we can determine how many inches the trees grew during the year of gardener’s care.
Oak B had more growth this year, so Gardener B is the superior gardener.
This is analogous to a Simple Growth Model, also called Gain.
We can compare the height of the trees one year ago to the height today.
By finding the difference between these heights, we can determine how many inches the trees grew during the year of gardener’s care.
By using this method, Gardener A’s tree grew 14 inches while Gardener B’s tree grew 20 inches. Oak B had more growth this year, so Gardener B is the superior gardener.
This is an example of using a Simple Growth Model, also called Gain, like FCAT learning gains that measure the change of a students achievement level or DSS score from one year to the next.

9. … but this simple growth result does not tell the whole story either.
We do not yet know how much of this growth was due to the strategies used by the gardeners themselves.
This is an “apples to oranges” comparison.
For our oak tree example, three environmental factors we will examine are:
Rainfall, Soil Richness, and Temperature.
But this Simple Growth result does not tell the whole story either.
Although we know how many inches the trees grew during this year, we do not yet know how much of this growth was due to the strategies used by the gardeners themselves.
If we really want to fairly evaluate the gardeners, we need to take into account other factors that influenced the growth of the trees besides the gardeners themselves.
For our oak tree example, three environmental factors we can examine that could impact tree growth outside the control of the gardener are: Rainfall, Soil Richness, and Temperature.

10. High Low Low High High Low
External condition
Oak Tree A
Oak Tree B
Rainfall amount
Soil richness
Temperature
High Low
Low High
High Low
Based on the data for our trees, we can see what kind of external conditions our two trees experienced during the last year.
Oak Tree A was in a region with High rainfall while Oak Tree B experienced Low rainfall.
Oak Tree A had low soil richness while Oak Tree B has high soil richness.
Oak Tree A had high temperature while Oak Tree B had low temperature.

11. How much the gardeners’ own strategies contributed to the growth of the trees…
We can take out each environmental factor’s contribution to growth.
After these external factors are accounted for, we will be left with the effect of just the gardeners.
To find the correct adjustments, we will analyze data from all oaks in the region.
Remember, the final goal is to determine how much the gardeners’ own strategies contributed to the growth of the trees.
If we can account for the impact of rainfall, soil richness, and temperature on the growth of the trees, we can then take out each environmental factor’s contribution to growth.
After these external factors are accounted for, we will be left with the effect of just the gardeners.
To find the correct adjustments, we will analyze data from all oaks in the region.

12. In order to find the impact of rainfall, soil richness, and temperature, we will plot the growth of each individual oak in the region compared to its environmental conditions.
In order to find the impact of rainfall, soil richness, and temperature, we will plot the growth of each individual oak in the region compared to its environmental conditions.
On the x-axis, we plot the relative amount of each environmental condition. On the y-axis, we plot how much each tree grew from year 3 to year 4.
Each dot represents a single oak tree in the area. By calculating an average line through the data, a line of average or predicted growth, we can determine a trend for each environmental factor.
From the data we collected for our region, we find that more rainfall and higher soil richness contributed positively to growth. Higher temperatures contributed negatively to growth.

13. -5 -2 +3 -3 -1 +2 +5 -3 -8 Rainfall Low Medium High Soil Richness Low
Now that we have identified growth trends for each of these environmental factors, we need to convert them into a form usable for our calculations.
Rainfall
Low
Medium
High
Growth in inches relative to the average -5 -2 +3
Soil Richness
Low
Medium
High
Growth in inches relative to the average -3 -1 +2
Now that we have identified growth trends for each of these environmental factors, we need to convert them into a form usable for our calculations.
We can summarize our trend information by determining a numerical adjustment based on High, Medium, and Low amount of each environmental condition.
For example, based on our data, we found that oak trees that experienced low rainfall tended to have 5 fewer inches of growth compared to the average growth of oak trees in the region.
Trees with medium rainfall tended to have 2 fewer inches of growth compared to the average.
Trees with high rainfall tended to have 3 more inches of growth compared to the average.
We can use these numerical adjustments for environmental conditions to account for their impact on tree growth outside of the control of the gardener.
Now we can go back to Oak A and Oak B to adjust for their growing conditions.
Temperature
Low
Medium
High
Growth in inches relative to the average +5 -3 -8
Now we can go back to Oak A and Oak B to adjust for their growing conditions.

14. To calculate our new adjusted growth, we start with simple growth.
Next, we will use our numerical adjustments to account for the effect of each tree’s environmental conditions.
When we are done, we will have an “apples to apples” comparison of the gardeners’ influence on growth.
To calculate our new adjusted growth, we start with the simple growth we calculated earlier.
Next, we will use our numerical adjustments to account for the effect of each tree’s environmental conditions. Essentially, we will be removing the effect of these factors.
After we have removed the effect of these external conditions, we will be left with the portion of growth that was due to the gardeners’ own strategies.
When we are done, we will have an “apples to apples” comparison of the gardeners’ influence on growth.
+20 Simple
Growth
+14 Simple
Growth

15. 3 inches of extra growth on average.
Based on data for all oak trees in the region, we found that high rainfall resulted in
3 inches of extra growth on average.
For having high rainfall, Oak A’s growth is adjusted by -3 to compensate.
Similarly, for having low rainfall, Oak B’s growth is adjusted by +5 to compensate.
Now each gardener’s “score” is adjusted to level the playing field for each gardener.
Points are added or subtracted so that the environmental elements no longer work to the gardener’s advantage or disadvantage.
Points are adjusted for amount of rainfall.
+20 Simple
+14 Simple
+ 5 for Rainfall
- 3 for Rainfall

16. For having poor soil, Oak A’s growth is adjusted by +3 to compensate.
For having rich soil, Oak B’s growth is adjusted by -2 to compensate.
Points are adjusted for the richness of the soil.
+20 Simple
+14 Simple
+ 5 for Rainfall
- 3 for Rainfall
- 2 for Soil
+ 3 for Soil

17. For having high temperature, Oak A’s growth is adjusted by +8 to compensate.
For having low temperature, Oak B’s growth is adjusted by -5 to compensate.
Points are adjusted for the temperature.
+20 Simple
+14 Simple
+ 5 for Rainfall
- 3 for Rainfall
- 2 for Soil
+ 3 for Soil
- 5 for Temp
+ 8 for Temp

18. We calculate that Gardener A’s effect on Oak A is +22 inches
Now that we have removed the effect of environmental conditions, our adjusted growth result puts the gardeners on a level playing field.
We calculate that Gardener A’s effect on Oak A is +22 inches
We calculate that Gardener B’s effect on Oak B is +18 inches
Now that we have removed the effect of environmental conditions, our adjusted growth result puts the gardeners on a level playing field.
What we are left with is the effect of the gardeners themselves.
We calculate that Gardener A’s effect on Oak A is +22 inches.
We calculate that Gardener B’s effect on Oak B is +18 inches.
+20 Simple
+14 Simple
+ 5 for Rainfall
- 3 for Rainfall
- 2 for Soil
+ 3 for Soil
- 5 for Temp
+ 8 for Temp
_________
+18 inches
Adjusted Growth
_________
+22 inches
Adjusted Growth

19. Using this method, Gardener A is the superior gardener.
By accounting for last year’s height and environmental conditions of the trees during this year, we found the “value” each gardener “added” to the growth of the tree.
This is analogous to a Value-Added Model.
Using this method, Gardener A is the superior gardener.
By accounting for last year’s height and environmental conditions of the trees during this year, we have found the “value” each gardener “added” to the growth of the tree.
This is an example of a Value-Added Model.
+20 Simple
+14 Simple
+ 5 for Rainfall
- 3 for Rainfall
- 2 for Soil
+ 3 for Soil
- 5 for Temp
+ 8 for Temp
_________
+18 inches
Adjusted Growth
_________
+22 inches
Adjusted Growth

20. Value-Added in Education
How does this analogy relate to Value-Added calculations in the education context?
Oak Tree Analogy
Value-Added in Education
What are we evaluating?
Gardeners
Schools/Principals
Teachers
What are we using to measure success?
Growth in Inches
Relative Growth in Scale Score Points
Sample
Single Oak Tree
Students
Control Factors
Rainfall
Soil Richness
Temperature
Students’ Prior Performance (most significant predictor)
Other variables collected for ALL students
ELL Status Retention
ESE/Gifted Status Class Size
Attendance
Mobility
How does this analogy relate to Value-Added calculations in the education context?
What are we evaluating? In the oak tree analogy, we evaluated gardeners. In the education context, we are evaluating teachers or schools.
What are we using to measure success? In the oak tree analogy, we measure growth in inches. In the education context, we measure relative growth in scale score points.
What about our sample? In the oak tree analogy, we only used a single oak tree per gardener. In the education context, we use students.
What do we control for? In the oak tree analogy, we analyzed rainfall, soil richness, and temperature. We were then able to remove their contribution to growth. We controlled for these factors.
In the education context, we control for prior performance. This tends to be the most significant predictor of student performance.
Based on what other data is available for ALL students, we also control for other factors beyond the district, school, or classroom’s influence, such as:
Free/Reduced Lunch Status English Language Learner Status IEP / Special Education Status Race Gender

21. To summarize - what is the difference between these measures?
All are based on student test data, but the results are analyzed in different ways.
Attainment
Gain/Growth
Value-Added
Evaluate based on student testing performance
Yes
Evaluate schools for meeting the needs of all students No
Hold schools accountable for what they can control
Comparing the different measures, Value-Added models meet our final goal of holding teachers or schools accountable for what they can control.