Cold call or MWB?

Cold calling* and mini whiteboards are both common features in many classrooms around the country, but when do you go for the mini whiteboards (MWBs) and when do you go for cold calling? Both techniques are good for building ratio in your classroom. At its simplest, ratio is the proportion of students who are on-task. Ideally you want all the students on task, but in reality that can be easier said than done. If students are allowed to not participate, they won't. It's easier not to. Students aren't being deliberately contrary. They generally aren't acting out of spite - "Sir/Madam want me to do X, so I'm not going to", but there is a possibility they're thinking (consciously or subconsciously) "Sir/Madam won't check if I'm doing X, so I'll take my time/do the bare minimum/not do it".

Cold Call
Cold call drags the ratio up - it increases the number of students who are on task - by making sure all the students are thinking about the answer before picking a student to actually give the answer. A good cold call has the following format: question, pause, name. By posing the question first, every single student in that room thinks they could be called on and it (hopefully) thinking of the answer. Pause to make sure they're all thinking of the answer, and then pick a student.
two timelines. The first says "Laura, what is the capital of COUNTRY?". A red line shows that the rest of the class stops thinking when Laura's name is said. The second line says "What is the capital of COUNTRY?....Laura?" The line shows the whole class is thinking until the point Laura's name is said, which is at the end of the question
We can clearly see in the graphic above - if cold call is done correctly, as in the bottom example - how long the other students are thinking.  [I have never in my life prefaced a cold call with "it's cold calling time". I just ask the question.**] Cold call is less well-suited for checking if 30 students know the answer. It is more well suited for making 30 students think about the answer. We know that retrieving information helps retrieval (Roediger & Karpicke, 2006). If you remember stuff it makes it easier to remember it again in the future. When you cold call, every single student (in theory) is retrieving the answer, or at least attempting to. This will make it easier for them to retrieve it the next time and the time after that and the time after that and the time in their exam. 
Because you're only calling on a couple of students, it does beg the question, which students do you pick? At my school, the first students should be the ones who are struggling, the canary kids. The ones who, if you call on them, will give you a pretty good idea if the rest of the class gets it. If they get it, it's likely the other 29 students in the room also get it. This is obviously not an exact science, and as you move from topic to topic, those students will not be the same every time. But you get an rough idea. If they don't get it, take a bigger sample - is it just them, or is it everyone?
Cold call is great for collecting answers. I consistently use it when students are self-assessing their work - "Okay, question 28, what is a catalyst........ Stuart?" - but I'll also spatter it throughout the non-independent practice parts of the lesson to bring students in, and to ensure think ratio is high.
When to use cold call: when you want all students to think about the answer, but you're not technically interested in everyone's response.

Mini whiteboards (MWBs)
MWBs are also good for building ratio, but in a slightly different way. Unlike with cold call, with MWBs, every single student is going to give you their answer, and therefore they are more useful when you want to check everyone's understanding (or at least most of the class). They are useful for times when you want to see a process, for example if they're doing a calculation, or balancing an equation. When using MWBs every student is thinking (because they all have to answer), but unlike with cold call, you are going to be able to check every student's answer. MWBs are great for the check and consolidate bit of the lesson. The bridge between the explanation and the independent task. It's a very easy way for (a) you to check that students 'get it', and (b) for students to 'have a go' before they're launched into the fully independent practice.
It can be tricky to get students to expand on other's answers when using MWBs because it relies on students having legible handwriting, but it is still possible.
NB: choral response is a useful alternative to MWBs for when you want a short sharp answer - "What organelle is the site of respiration?" [As a class] "mitochondria".
When to use MWBs: when you want all students to think about the answer, and you want to know what they all thought.

In my classroom, students will be cold called to give answers to the Do Now, I will then explain something, then before students go onto their independent work, we'll do a QDC&C (Boxer, 2021) on MWBs so I can check they get it and they can have a practice before doing it in their book.


*Cold call is a questioning technique from Doug Lemov's Teach Like a Champion. A question is posed, the teacher pauses, then names a student. The key part is this happens without taking hands up.
** "It's cold calling time" reminds me of that "It's Chico time" does anyone remember that?

Boxer, Adam (2021) Teaching Secondary Science: A Complete Guide; John Catt Educational
Roediger III, H. L. & Karpicke, J. D. (2006). Test-enhanced learning: Taking memory tests improves long-term retention. Psychological Science, 17 (3), 249-255
Cold call diagram by Luke Tayler