An ELT Glossary : Open and Closed Pairwork
Pairwork can be done either in open pairs, where two students do an activity in front of the class while the others listen, or in closed pairs - when all the students are working on an activity in pairs at the same time.
Open pairwork is a useful way to start some activities - it checks that students have understood what they have to do and provides them with a model. For example, the T might set up a What do you say? activity on polite requests in the following way. The students have the prompt situations in their books :
T : OK everyone - look at situation number 1: You're trying to study but your flatmate is playing music very loudly and it's disturbing you. Maria, what do you say, and Paolo, what do you reply?
M : Sorry Paolo. Can you turn the music down? I'm trying to study.
P : Oh OK, sorry.
T : OK, great. All right, now can you all continue with your partners. Decide what you say in those ten situations.
Having elicited the example in open pairs, the teacher now asks the students to continue the activity in closed pairs, which maximises student involvement and ensures they get as much practice as possible. S/he will probably monitor them while they are working, but in a large class won't be able to hear what everybody says for every situation. So at the end s/he may follow-up the activity by going through all the situations again in open pairs, confirming or correcting their answers, and giving them the chance to ask questions about any alternatives they came up with.