How long you use immersion before speaking in English with your students depends on your school schedule and your students. At my first full-time teaching position, the school year started on a Wednesday, so we had a three-day week followed by a five-day week. I saw my French 1 students every day for 45-minute periods. At that school, I used immersion Wednesday through Friday, then had my English week the following week. 

At that school I also taught an exploratory class and the length of the introductory immersion experience and the English discussion for those classes was different, though. My Spanish colleague and I shared students: I saw a group of students for half a quarter, she saw a group of students for half a quarter, then we switched. With such a short period of time with those students, I did two and a half days of immersion before speaking in English for the first time. The second half of the third day was our very abbreviated English discussion. 

At my next school, we started the year with a split start where we saw the first half of the alphabet the first day and the second half the following day. Plus, we had block scheduling, so I did not see half of my students until the third or fourth day of school. Because of this, I extended my immersion period to be much longer. I wanted all students to have at least three full class periods using immersion, so that they start getting the hang of figuring out what’s going on without expecting me to translate what I’m saying into English. 

You can do more than three full class periods, too. For some of my classes one year, I did not start English week until the third week of school. I wanted those classes to get used to immersion a little more before using English. (I will say that I think in general it is better if you start English week with all of your classes at the same time because word does get around that you actually do speak English, but the immersion experience is so important that I decided to risk it for those classes.) 

Another benefit of waiting several days before speaking in English is students who may be considered “problem students” are more likely to drop your class. These are the students who are unwilling to tackle any sort of challenge at all. Let them be scared that your class will be too hard and decide to take a different elective. However, don’t worry if there are quite a few resistant students those first few days. That is completely normal. After several days of immersion then a full week of English, those students will be more willing to try because they know they can get meaning out of your class even with immersion and they understand the why behind how you teach.