I love a good student lab. (I usually do around 40 of them in a school year.) Chemistry is a hands-on science, and students should have plenty of opportunities to actually do chemistry instead of spending the entire year watching someone else do it. But not every experiment needs to be a student lab.
Sometimes, turning an activity into a teacher demonstration and having students complete a mini lab report based on their observations is the better instructional choice. You can still ask students to make predictions, record data, analyze results, and draw conclusions without putting a set of chemicals and equipment at every lab station.
So how do you decide? Here are the biggest things I consider when choosing between a full student lab and a teacher demonstration.
How Much Time Do You Have?
Student labs take time. And I’m not just talking about the actual procedure. You have to distribute materials, explain the setup, get everyone into groups, answer the same question at six different lab tables, clean everything up, and inevitably deal with the group that is somehow still on Step 3 when everyone else is washing their glassware.
Rinse and repeat for the rest of your classes for the day.
A 10-minute procedure can easily consume most of a class period. If students need the hands-on experience, that time is absolutely worth it. But sometimes the goal of the activity is simply for students to observe a chemical phenomenon and interpret what happened.
In that case, a teacher demo can be much more efficient. You might be able to complete the experiment in 10 minutes, then give students another 10-15 minutes to finish a mini lab report. They still practice making observations, analyzing evidence, and connecting what they saw to chemistry concepts, but you haven’t sacrificed an entire class period.
How Much Material Will the Lab Use?
This is a BIG one in chemistry! Especially if you’re working in a non-lab room.
A demonstration performed once at the front of the room might require 10 mL of a solution. Turn that same procedure into a lab for eight groups and suddenly you’re preparing 80 mL, plus extra because someone will spill something, contaminate a dropper, or enthusiastically pour four times as much as they were supposed to. Again, rinse and repeat for the rest of your classes for the day.
For inexpensive materials, that might not matter. For expensive chemicals, specialized equipment, or materials that are annoying to prepare, it absolutely does matter. Before turning an experiment into a student lab, ask yourself whether students actually gain something important from physically performing the procedure with their own hands.
If the learning comes primarily from what happens, rather than from doing the technique, a demonstration may make more sense.
How Safe Is the Procedure?
Obviously, safety should always be a consideration in the chemistry classroom. There are plenty of experiments that can be performed safely by a trained chemistry teacher but become significantly riskier when 30 teenagers are performing them simultaneously.
Consider things like:
- Open flames or high temperatures
- Concentrated acids or bases
- Toxic or irritating chemicals
- Side reactions that may occur in a waste beaker
- Reactions that produce fumes
- Pressurized systems
- Procedures requiring especially careful handling
- Reactions that can become dangerous if students use the wrong quantity
This doesn’t mean students should never work with anything more dangerous than baking soda. Part of learning chemistry is learning to work safely in a laboratory. But the risk needs to be justified by the educational benefit.
If students need practice using a Bunsen burner, then using the burner themselves matters. If the burner is simply being used to heat something so students can observe the resulting reaction, they may not need to be the ones holding it. Or maybe a swap to a hot plate is better! There are times when the correct answer for safety is a lab procedure modification, and times where it’s best for the teacher to do the demo.
There are times where even I don’t like the materials a lab requires for safety reason. (I’m thinking about the classic: Group 1 Reactivity Trend.) YouTube videos are also an amazing alternative to traditional labs or even demos when the materials call for it.
Is the Lab Teaching a Skill or Demonstrating a Concept?
This may be the most important question. Some labs are valuable because students need to learn how to do something: light a burner, tare a balance, filter a mixture, create a standard, run multiple trials, read a burette… the list goes on. Those should usually be student labs.
Other labs are valuable because students need to see something happen. Maybe you’re demonstrating conservation of mass, showing an especially dramatic reaction, comparing reaction rates, or giving students evidence they will use to identify an unknown. In those cases, physically pouring the chemicals themselves may add very little to the learning objective. That’s a great opportunity for a demonstration.
How Complicated Is the Setup and Cleanup?
Sometimes a lab isn’t difficult for students at all. It’s difficult for you. If a student lab requires you to prepare eight identical setups, label dozens of containers, portion chemicals, organize specialized equipment, and then clean everything afterward, consider whether that preparation is worth the instructional payoff.
One teacher demonstration might give students almost the exact same academic experience with a fraction of the prep. And teacher time counts, too. You don’t earn bonus points for spending your entire planning period filling 32 tiny cups with 2 grams of the same chemical when one demonstration would accomplish your objective just as effectively.
Now at some point, taking on a TA, might save you the time and give you an opportunity to turn demos into labs. I’ve never had that privilege, but it’s something to consider!
Making Teacher Demos More Than a Show
The biggest danger with teacher demonstrations is allowing students to become passive observers. Don’t just say, “Watch this!” Give them something to do with what they’re watching.
I like the idea of having students complete a mini lab report. Depending on the experiment, students might record:
Purpose or Question: What are we trying to determine, observe or learn?
Prediction: What do you think will happen?
Observations/Data: What did you actually see?
Analysis: What does the evidence tell us?
Conclusion: How does this demonstration connect to the chemistry concept we’re studying?
You can even have students create a data table before the demonstration or require them to sketch the setup. Now the demonstration isn’t just entertainment. Students are still practicing scientific thinking without every student physically conducting the experiment. You get to be your student’s lab partner!
You Need Both
Student labs and teacher demonstrations don’t have to compete with each other. Students absolutely need hands-on laboratory experience in chemistry. They need to learn how to measure, manipulate equipment, follow procedures, troubleshoot mistakes, work safely, and collect their own data.
But hands-on doesn’t automatically mean better. Sometimes the best use of a class period is letting students perform the experiment themselves. Other times, the safest, fastest, cheapest, and most effective option is to perform the experiment once and let students focus on analyzing what happened.
The real question you need to ask yourself is: “what do my students actually need to get out of this experience?” Once you know the answer to that, deciding between a student lab and a teacher demo becomes a whole lot easier.
PS: If you need it, I have two free lists of demos that I like to use in my classroom. Here’s some for Intermolecular Forces, and a list for Kinetics & Equilibrium.
