The Role of Labs in PBL


A couple years ago, I wrote this piece for other science teachers in the New Tech Network.  I believe that it still holds true, but it is interesting, because all the examples are scenario-based projects, reflecting a moment in time regarding my practice, and my view of PBL.

While building and planning labs into projects might seem to be a challenge, I believe it crucial that labs are part of teaching science, whether you use PBL or not, for all sorts of reasons.  Here is a list of some of those reasons: 
  1. It’s just good science teaching practice.   Students in science classes should act as scientists, making observations, hypotheses, and generating experiments.  The best way to do this is through labs.
  2. Particularly through inquiry-style labs, interaction with physical things affords opportunity for critical thinking that is different than other group work.
  3. Labs provide an opportunity for face-to-face collaboration, and a chance for the teacher to assess collaboration.
  4. Students in science classes typically identify labs as their favorite part – hence labs are a way to increase engagement.
  5. Many districts mandate that science courses must spend as much as 40% of class time doing lab-based activities.

In projects, lab activities should play a crucial role in scaffolding student understanding of the scientific concepts, and you can do it in a variety of ways.  Here are three different approaches, with illustrative examples, using some projects I’ve developed, and others that colleagues of mine have developed and run.

Again – the examples are scenario-based projects, because I wrote this some time ago, when scenarios were the bulk of my repertoire. Not sure what I mean when I say “scenario based”? Here’s a pretty good description.  In comparison, here’s something about scenario-based vs reality based, and here is something on the other end of the spectrum.  I think I may create a Part II to this posting.

Approach 1:  Labs Are Required for Final Product

This is the most sophisticated and elegant way of integrating labs.   The project design, often times in the entry document (or early in the project), prompts students to explore something in the lab, so that the data that they collect will be used directly in the final presentation or product.
Example Physics Project:  Gothos Ex Machina
In this slightly fantastical scenario-based project, students play the role of engineers in Gothic Europe, trying to understand how the Romans lift heavy things.  There is a picture of a pulley in the entry document. The end presentation is trade-show style, where teams of students set up their pulley systems and explain to wandering assessors their understanding of pulleys.
Lab:  Students must experiment with pulley systems, and figure out how to make them, which allows them to construct an understanding of conservation of energy (Energy as Work, in this case).   Work on the pulley system with measurements takes up about two thirds of the class time for this project.
Example Chemistry Project:  The Case of Toxic Waste
Students as consultants to the EPA must determine how much pollution three different sources are dumping into a local river and whether the sources are in compliance with law.  They are given data from the river; however, it is not all complete, as you can see from the column entitled “pH”. 


Lab:  Students must measure the pH of “river samples” gathered each day that the instructor provides.   The instructor concocts the samples such that the sample from one day is more acidic than the others, which will indicate that the polluter at Source 3 is out of compliance with the law on one particular day.

Approach 2:  Labs Address the Same Standards as Project, but data isn’t used directly in final product.

In this approach, a project creates a need to know a standard, but it might have been too difficult to integrate a lab seamlessly like the above examples.   However, if there is a lab that illustrates the same standard as the project addresses, it is perfectly ok to run that lab in the project, even if the data won’t be used directly in the final product.   In fact, it is better to run the lab than not.  
Example Chemistry Project:  Element Speed Dating
In this project, students play the role of an anthropomorphic element looking for another element with which it is compatible.  The final performance is a “speed dating” session where students-as-elements interview each other to find possible partners.   This project addresses periodicity and chemical & physical properties.

Lab:  The entry video for this project does not call for a lab or data specifically.   However, a teacher running this could use any number of standard labs that illustrate periodicity; a classic version has students observing properties in common between Li, Na, and K, (all group 1 elements) and then properties in common between Ca and Mg (group 2 elements).
Example Physics Project:  Moongames
Students play the role of game designers, charged with inventing a game to be played on the moon by colonists.  In their game design, they need to take into account the behavior of objects as described by Newton’s three laws.  The final presentation has them presenting their game to a panel.

Lab:  In order to illustrate Newton’s 2ndLaw (a a F/m) a teacher might use a classic lab where students attach a string to a cart, and place weights on the end of the string, so that the cart gets pulled along a track with a constant force.  Students can then experiment with the effect of mass on acceleration, and force on acceleration.  Results from this lab are probably not used directly in the final presentation, but they know from the lab what mass and force will do to acceleration, and then can apply that knowledge to their work on the final product.

Approach 3:  Lab As Mini Project or Problem-based Unit

Sometimes the standards for a class are ripe for illustration with a lab, but are difficult to fit into a standard multi-week project.   In this case, teachers have found it propitious to create a narrative around the lab that provides a connection to the world outside the classroom, and/or creates a need-to-know the ideas of the lab.    In this case, the execution of the lab can be the performance or final product, or the teacher can add a follow-up activity to complete the solution of the problem.

Example Chemistry Lab/Mini Project:  Bag the Tagger

In this mini-project, students play the role of school detective, who must determine the identity of a culprit who has tagged several rooms and textbooks at the school.  Students receive a group of black markers, and pieces of paper with samples of the tagging.   This project is meant to deal with separation techniques (chromatography) and properties of water (polarity, hydrogen bonding, solubility).   Students present their findings to the class in a mock trial.   This mini-project would take about 4-5 days.

Lab:  As a scaffold, students first carry out a recipe-style lab where they learn techniques of Chromatography with both water and acetone.    As a second lab, students are given pens gathered from a variety of “suspects”, and “samples” from the text book, with writing from one of the pens on them.  Students must create their own test to determine which pen did the writing.

Example Physics Lab/Mini Project:  Me Tarzan, You Jane

A great lab to demonstrate Conservation of Mechanical Energy includes a set-up with a weight swinging on a thread, which is cut during the swing by a razor blade, resulting in the washer free-falling to the ground.   Students place a target on the ground, based upon their measurements of the apparatus and subsequent calculations, then release the weight to see if it lands on the target. 


The narrative:  The weight is Tarzan, the thread the vine.   Tarzan must successfully swing on the vine, which, in mid-swing, is cut by a razor sharp Tucan’s beak – which will send Tarzan flying and hopefully land on an island (target) where Jane is marooned.  Of course, the island is surrounded by piranha. 

In this case, students perform the lab, and submit their derivations and calculations as a lab write up, and the project is over.  No, not terribly authentic, but extraordinarily engaging to the students.

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