Science Snippet 1: Growing a Question Tree

Question trees can be really useful aids for pupils to work logically through a process and build up both declarative and procedural knowledge while being supported in their thinking. They provide an opportunity for pupils to deepen their understanding independently as they progress through a task.

This week my Year 10 class were having a lesson on testing for carbonates and sulfates and this is how it went!

Growing the Question Tree

Happily, growing it is much quicker than growing a mighty oak but in the same way you may be intimidated when being asked to clamber up to the heady heights of the canopy a pupil could be overloaded by the complexity of the question tree. For this reason I chose to grow the tree slowly alongside demonstrating the chemical tests the pupils would be using. I’ve use my visualiser for as many practical demonstrations as possible as pupils are better able to see what is happening (zoom function) and managing behaviour is sooooooooo much easier!

Solid or Solution? I wrote that the first test is to ‘add a few drops of HCl’ then showed this test on some magnesium carbonate using the visualiser. Several of them exclaimed “Oh, it bubbles” and one clever cookie stated “effervescence”. We then added this to the tree.


I told them that the gas produced was carbon dioxide and asked them to suggest how this could be proven; answers on whiteboards mostly showed “limewater goes cloudy”. We had a gas tests lesson a couple of weeks back so a handy retrieval opportunity. This then leads to the conclusion that carbonate must be present. If there are no bubbles or the limewater doesn’t cloud then we would have use a different test.


Solutions Next…

Next I tell pupils that we will investigate what happens when a carbonate is in solution with the first step being to add a few drops of hydrochloric acid again. I ask them to predict what we might be looking for (bubbles), how we could prove their identity (limewater again) and therefore what anion is in the solution. Using sodium hydrogen carbonate I showed them this on the visualiser and we added the information to our tree.


Then I lead them through the test for sulfates and we briefly discuss that if the acid doesn’t cause effervescence and with barium chloride a white precipitate doesn’t form then it must mean we have a different anion (we are doing halide tests next week!).

We add our final bits of information to our question tree so it is ready to use in their investigation.


In total, the demonstrating and building up of information took about 12-15 minutes, quite a bit longer than giving them all the equipment, the full question tree and saying “crack on kids”!

By gradually growing the tree of knowledge the working memory isn’t overloaded. As I lead them through the process writing, asking questions and showing the chemicals doing their business they are able to build schema at a manageable rate.

By asking questions and explicitly linking new learning to prior knowledge the two become more strongly linked and more memorable. Knowledge will be more durable and flexible.

By switching between writing about the process then demonstrating it (you could do this on the whiteboard if you don’t have a visualiser) so only writing is visible or the reaction is visible with (my words in their ears) pupils benefit from dual coding.

This concluded my modelling of the process.

Will the Tree Bear Fruit? Time to Practise

Armed with their question trees and eye protection, I asked pupils to identify the anion found in 4 mystery solutions and then write a justification for their results.

This practical was like no other that I can remember. The question tree guided them in their practise so I didn’t have to!

For about 15 minutes I just walked around and watched them work. I didn’t have to tell any of them what to do next at any point due to the cognitive support provided by the question tree. Due to not being overloaded by the amount of information in their question trees they could navigate the experiment successfully. The most dramatic incident was a test tube falling out of a test tube rack and on to the floor.

They finished early. By the time the last pair had put away their equipment and gone back to writing justifications there was still 1:40s left on the timer!

I grabbed a pupil’s book and popped it under the visualiser, froze the image and gave it him back. We then spent a few minutes critiquing his explanation with me editing on the board where the image is displayed to show what a good one looks like. Then we had silent writing where I could wander round and offer support and suggest improvements. After what felt like enough time I selected pupils to read aloud their work as feedback, allowing pupils to make corrections/additions to their own writing.

Knowledge Blossomed: Quick Review

  • Using the visualiser and live drawing the question tree with pupils following along helped avoid cognitive overload.
  • Dual coding was achieved by switching from growing the question tree and showing the chemical tests (I flipping love my visualiser!) while I explained what was happening.
  • The clear, explicit modelling of the tests with questions helped reinforce prior knowledge and check for understanding.
  • The cognitive support provided by the question tree meant they could deepen their knowledge through successful practice.
  • They had independent practice of the knowledge while writing their justifications.

In the next lesson we will test for halides and following that we will tackle some questions which interleave each of the different chemical tests for cations, gases and anions. High challenge, high impact.

As always please do comment, share and challenge and if any of you can share useful knowledge from your own experiences that would be gratefully received!

You can follow me on twitter if you like. @MrTSci409


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s