The Value of "Labs"

In a post below, Catherine questioned the value of laboratory time in science classes and implied that it was constructivist in the same way as "guess and check" in a math class.

"She was least behind in the sciences, which makes sense to me because science education became progressive many, many years ago and has remained so to this day. This is why science has always had 'labs.'"

I don't think this is inherently true. In fact, I think that well-conducted labs are crucial to a real science education.

When done poorly, labs take an hour to teach what could be taught directly by the teacher in 2 minutes ... and labs are often done poorly. One of the signs of a poorly conducted lab is that the lab is being used to teach the facts of science. You don't need to cut open a frog to learn that a frog has lungs.

Done well, though, labs teach several things that lectures do not teach well:

Lab Technique

Measuring difficult things, making notes, interpreting results, and producing a lab report that presents those results are useful skills. Like many other skills, they require practice. But I don't really want to do dissections on the dining room table and energetic reactions in the kitchen. The time and space required to learn these skills is only really available in a laboratory during school hours. Home is a poor substitute.

These skills are exactly the sort of skills that are broadly useful for life. I assert that they are entirely appropriate for a general education.

Accuracy and its Limits

Your lab results aren't going to match the ideal results. Oh, you might get lucky once and have your mean result end up fairly close to the mean expected result. But it requires good technique and a bit of luck. Without both, you are likely to end up proving that the third law of thermodynamics is all wrong. Understanding how this happens and what can cause it is pretty important.

But even if you do everything right, you won't end up with the precisely correct result. The canonical result is a statistical construct accurate only within some error band. Understanding that this is true for your experiments and for the experiments you read about in the newspaper is critically important.

Statistics and error bands are hard to understand, and a personal attempt that results in statistical results with a broader error band than you'd prefer can be useful. This must be followed, of course, with direct instruction of why this happens and what it means. But I think it best to begin with a practical demonstration.

Honesty

If your lab results do match the "expected" results too closely, your teacher should be questioning them. It's more likely that pristine results are caused by cooking the books than by cooking the chemicals just perfectly. Again, this might be a universal truth.

If your answers weren't right, and you report them honestly, your results should be treated with respect. Of course, any such result should include your best estimate of what went wrong. (It's probably not the science. 8-)

In too many cases, of course, the grade depends not on good science, but on a result that matches the canonical result. I consider that to be scientific malpractice.

Troubleshooting

On the other hand, if your answers are a complete mess, it can be very useful to run through the process of determining where you made your mistakes. To do this, you need to know what the expected result was and how experimental errors could have caused bad results. This requires a fairly deep understanding of the science, and probably requires direct help from a more knowledgeable source, at least in the beginning. Again, this sort of practice has significant real-world value.

Scientific method

Observe, hypothesize, test, theorize, identify falsifying criteria, test for falsification, modify theory. The process is both rigorous and useful, and not just in science. But to see it in action, you have to do it. If you only ever do experiments where you know what to expect, you'll never get to see this powerful tool in action.

Unfortunately, this isn't the practice in most HS labs. Some labs for every student should ask interesting questions and let the students find out the results. I view egg-drop experiments in this category, but not as they were done for C. When done well, a negative result is just as important as a positive result.

If you find that embedding an egg in jello is ineffective in dissipating kinetic energy, that's just as valid a result, and just as worthy of points, as finding out that parachutes work well.

Proof of the Unusual

Some concepts are very difficult to understand or believe. For at least some of these, a demonstration can be very useful. For example, torque is deeply counterintuitive -- until you've seen a spinning wheel supported only at one end and not falling over, you probably just won't get it. Once you do see it, you probably won't forget it. And, of course, for a visceral [1] understanding of what the inside of a creature is like, there's nothing better than a dissection.

Advice

As I see it, then, to get value for time in a laboratory, a teacher must do the following:

• Identify the course content that is best taught in a lab rather than in a lecture.


• Identify the goal or goals of each individual lab experiment.


• Evaluate your success in meeting those goals.


• Remediate the failures as soon as possible.


• Reinforce in lectures the lessons that you intended to teach in labs.


• Grade lab reports that have the wrong results the same as labs that have the correct results, as long as the student cogently discusses both the deviation from the expected results and the probable reasons for that deviation.

Let me reiterate that I don't think that labs are a good way of teaching scientific content -- with the limited exception of a few counter-intuitive cases. But I think that labs are crucial to teaching science.

[1] Sorry; couldn't resist.

Update: Added sixth bullet to "Advice" as recommended by Tracy. (Thanks!)