Friday, August 18, 2006

About that "weighing the pig" analogy....

Many of you know the "you don't make the pig grow by weighing it" analogy and have heard it applied to NCLB testing requirements. That's bugged me for quite some time as a pretty weak statement. I'm not a fan of testing for no reason and I hate tests that are not aligned to the education system's learing goals. Poorly aligned tests provide the worst sort of incentives and almost no vaulable feedback.

However, I still have a problem with this analogy. Let's think this through. I wouldn't want to compare education to fattening a pig for market. What do we know about pigs?
  1. The growth trajectory of a pig from birth to slaughter weight is a pretty well understood piece of meat science. For more info specialization in this industry see the USDA background brief on hog farming.
  2. Pigs have range of growth rates that is well understood. The grow at well understood rates throughout different periods of their maturation. The farmer only needs to provide food and water.
  3. While weighing the pig does not make it go fatter, you better believe the farmer weights the inputs to pig growth (feed) very carefully. Farmers know very specifically how much of which kinds of nutrient sources a pig needs throughout its life cycle. It is in the farmer's interest to do this well and consistently through all stages of growth.
  4. The growth characteristics of a pig are inherent to the pig. The only time the pig needs to be weighed is at time of sale to get the overall purchase weight. If the farmer does the production right, the pig will weigh what it is supposed to weigh at the time of sale. The weighing is about the commercial exchange between farmer and buyer.
What about student learning?
  1. The growth trajectory of child learning is known and taught in child development courses, but we also know that there is great variance. We don't just want to get a child to some arbitrary amount of learning based on the child's characteristics. We have societal norms about what is expected for participation in a democratic society.
  2. The growth of children is affected by the peer group. Pig A does not grow faster or more slowly if Pig B is a slower or faster learner. Peer effects in classrooms and schools is profound. One could think of this as one of the inputs to learning that we don't know much about.
  3. The pig will grow if the farmer is poor or rich, black or white, if she likes or does not like pigs, etc. Kids learn better if they have supportive parents, come from homes with adequate resources, speak English well, etc. The thing pigs bring to the pen don't affect the pig's growth (apart from genetics around size itself).
  4. We know almost nothing about the inputs to education - at least compared to our farmer. When we look at how much a student has learned, an enormous number of factors enter in to explain the variation one sees across the population. We collect almost none the data one would need to understand that variation.
  5. The one thing we seem to have in common is the notion of the buyer weighing the pig/student. We publish test scores for schools and districts as a way of telling the buyer (taxpayers and voters) what they got for their investment in public education. That's about the only similarity I can see. Particularly since, we as citizens have already paid for the education at that point. This is a retrospective look to see what we eventually received for what we paid up front.
All in all, I don't see that the analogy holds much water.


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