hit counter joomla

The blood typing lab, part I. What went wrong? and why?
Blood typing part II. Can this laboratory be saved?

Those wacky non-major Zoo students are at it again! And this time they drew blood!

Mike’s undergraduate students learned about blood typing, a common tool of detectives and real crime TV. They did the classic blood typing lab, and by golly, they refused to parrot the correct answer on the test! The nerve! After all, he pretty much told them the answer and even used the exact same wording that was used on the test question. Why didn’t the students just memorize it and regurgitate?

Can a scientific approach to teaching can help us out?

How do we do that?

First, a quick summary of the class activity:
The students pricked their fingers and determined their own blood types. Mike told them that a mother with type AB blood could not have a child with type O blood. In one section of the class 25% of the students got the question wrong, in the other section 20% got it wrong.

Q: What were the experimental treatments?

A: 1. The students did an activity with blood typing.
2. Their instructor shared verbal information.

Q: What was the expected outcome?

A: I’m not certain, but I think Mike expected all the students to get the right answer.

Q: What was the actual outcome?

A: Between 75 and 80% of the students got the correct answer on the test.

What do we do next?

What do you when an experiment doesn’t work the way you expected?

A: Hmmm. I try to figure out which step went wrong and then I try to find out why it went wrong.

How do we do that? What can we try?

We can start by reevaluating our assumptions and expectations. Were they correct?

1. Assumption one: Too many students (20-25% in the two sections) got the question wrong.

And 75-80% of the students got the question right. Is that abnormally low? Mike could look at historical data and query other people who’ve taught the class. If it were me, I would be satisfied with those numbers, especially with non-science majors.

You’re not very much help. Mike wants to do better! Is there anything else can we learn?

It would be helpful, for future classes if nothing else, to know why students are getting the wrong answer. Mike could survey, or interview, the students, who gave incorrect answers and try to find out what happened.

I think he would find that students fall into the following groups:

1. Those who weren’t paying attention or didn’t do the assignment.
2. Those who didn’t understand the question.
3. Those who got the question wrong but can’t explain why (probably because they haven’t learned how to speak “biology.”
4. Those who got it wrong and can articulate the reason.

The last two groups could provide some help in identifying specific things that got them off track, but it does take time to develop the interviewing skills that help you get at the information.

Let’s tackle the second assumption.

What second assumption?

See if you can guess it from my selectively chosen quotes:

I did a lecture prior to the experiment, and went over blood group inheritance. I went over blood group inheritance again with students on a one-on-one basis during the experiment, while looking at their results.


At the end of that, I reminded them that an AB parent couldn’t have an O child…

Okay, here’s the answer:

Assumption two: Telling students the correct answer will cause them to give the correct answer on a test.

There are other methods of teaching that are known to be more effective than “telling the students the answer.” I’ll come back to those later on.

Mike even did a small pilot test, and used a different teaching method with 25% of his class:

.. had about a quarter of the students tell me what their blood type was, and what bloodtypes their parents could not have.

Making students explain concepts in their own words is a well-established and validated method for reinforcing learning, plus it gives the instructor a nice assessment tool.

This is another place where we could use a scientific approach. If Mike had jotted down the names of those students, we could ask if those students did better, worse, or the same as the students who weren’t asked to state their conclusions out loud and explain their answers.

There is a large body of research that shows that students learn and understand concepts better through methods of active and/or inquiry-based teaching than they do from being told the answer. These methods involve having students interact with the material through activities like:

* having students state the problem and answers in their own words,
* having students complete problem sets and homework,
* using lab activities that guide students towards discovering the answer themselves.

How could we add some active-learning methods to the blood typing activity ?

If you have ideas, jot them in the comments. Or check back later and I’ll show you mine.

technorati tags: , ,


  1. #1 Bardiac
    October 7, 2006

    It seems to me that one of the problems with the lab and quiz is that the lab doesn’t teach what the quiz purports to test. That is, there’s no way for students to learn anything about blood type inheritance by typing their own blood alone. They’d have to type their parents’ blood, siblings, and then maybe make up charts to show the array of inheritance for the whole class. (They might learn about safe blood technique, but is that the point? And I doubt they’re actually learning about the testing mechanism identifying the blood type, are they?)

    The blood type inheritance question seems to be expecting students to have two types of knowledge, one about dominance in genotype/phenotype, and one about the specifics of blood typing.

    Maybe it would be worthwhile to start with something familiar to make sure students understand dominance, something as simple as rock/paper/scissors. That simple game helps students see that dominance is relative.

    Then maybe make up “gene cards” in different colors for blood types: A gets blue, B gets red, say, and O gets white. Establish that red and blue are equally dominant relative to each other, and each is dominant over white. Then give each student two random cards, and have him/her identify the genotype and phenotype. Red and blue make purple, so AB, and so forth.

    Once they can do that, then have two students get together to combine one card from each randomly, and have them identify genotype and phenotype.

    They could also systematically test every possible combination for any two students’ gene cards and make up a chart. Then group them up and have them compare charts. Have them use highlighters, maybe, to express phenotype?

    It’s an off the top of my head sort of exercise, but it would get students physically involved (which can help learning), give them practice thinking about genotype/phenotype, and actually let them visualize the blood types.

    One of the difficulties in teaching is that most of us were good at being students of our subject, so it’s difficult for us to think about communicating with people for whom our subject isn’t “easy” or “intuitive.” I think more experienced teachers learn to analyze the skills they’re teaching and to break those down into more teachable bits. But it sure takes time!

    Now I’m interested to see your proposal!

  2. #2 Sandra Porter
    October 9, 2006

    Hi Bardiac:

    Thanks for your comments. Learning how to communicate with students is a skill that does take time (and constant reminders) to develop.

    I suspect that you’re right that the test questions are misaligned wih the class activities. Blood typing is kind of fun but there are quite a few parts to this procedure that can overwhelm students who are new to biology.

    I think one of the problems with the test might have been due to the kind of question. The format: “which situation can’t happen?” is a much harder question than asking which option is the correct answer.

    As far as your idea with the gene cards, I would use a similar approach – and now it’s posted. : )

New comments have been temporarily disabled. Please check back soon.