With that set-up you’re not there to teach. You’re there to be the token foreigner to prove how progressive their school is.
50 minutes per week per class, 50 students per class = 1 minute of your time per student per week for the one thing that you can do better than a local teacher, which is to interact with the students so that they have exerience of talking with a native speaker.
You’re losing control because they’re bored, because they’re not participating in the class. If they can’t answer “what is your name?” then what hope have they of following you through the book? Most are going to have no idea what you’re talking about and as their previous experience of education has been all about memorising the answers the whole period with you will be a bewildering and uninteresting time. Not your fault, but that’s how it is.
Do you physically have space for group work? Can you control the groups, I mean keep discipline? Do you have a TA?
In your position the best thing might be to create worksheets based on what’s in the book, or work out a formula for getting through the bookwork that will keep everyone occupied. You have to keep them busy at something they can achieve. Some form of game or competition can keep them focused. Remember that someone else has already taught them the grammar and vocabulary. Your job, if anything, is to reinforce it and make them use it.
Do you take a roll call? That can easily be ten minutes of class time, and fun. Force them to find new ways to answer. Write each reply on the board and keep a total of how many times it comes up. Set a limit. Pretty soon they’ll be answering with Aloha teacher, yo, my name is Johnny, and more.
Have them read dialogues or reading passages in groups. Half the class is George and half is Mary, or each row of kids reads one line of dialogue. Getting underconfident individuals to read aloud won’t help much, but you could have them each read just one word. It’s amazing how hard it is for some kids to do even that. They’ll be a lot more confident in groups, just insist on them being loud enough. After you go through it a couple of times you can spice it up by, for instance, counting out loud while they’re doing it. Every time you reach some pre-determined number the group that is speaking has to perform some forfeit. Stand up, stand on your chair, stand on one leg, whatever. It focuses their minds on the reading, and once they’re into it you can insist on proper pronunciation.
I used to do the first few questions of each section, to model the answers and to give the more advanced students the chance to show off. I also pick people at random and push/guide them through giving me the answer. If they can’t do it you need to know who the smart kids are that can help them while you accidentally turn your back, but make the kid you chose read you ‘his’ answer.
Allow a set amount of time for each section, and after you’ve done the first few Qs you have a bit of time to walk around and look at people’s books. Have them finish it for homework, and move on to the next section.
Also, and this worked wonders for me, you have to keep a record for every student. I make up an excel sheet of student names and numbers with columns for their bookwork grades. There’s an additional column for their classwork grade, which I set initially to whatever the pass grade is, say 70%
Print 2 copies, give one to the class leader every week - or to the home room teacher.
You don’t need to collect books in. Check them while they’re doing bookwork in class. You don’t have to see every book every week. Just look at your list and pick the students you don’t have grades for. Mark the work, write the grade on your sheet, and type it up later. It takes five minutes per class. and can automatically calculate running averages for each student.
If a kid doesn’t have their book, hasn’t done homework, etc then deduct points from their classwork grade (one per offence) and make a note to check that kid the following week. If they talk in class, goof off, etc then deduct points. If they volunteer answers - even if they’re wrong - then add points. Give points for good homework, interesting replies when you call the roll, anything that indicates effort. You can even assign someone to keep score for you.
Pretty soon they will see that their initial pass grade is turning into a fail or a merit and that they have the power to change it even if they aren’t very good at English. In making the effort to keep you happy they’ll hopefully actually learn something too. You can also set objectives such as an average grade for the whole class that will earn them some reward such as a games class or no homework for a week.
This is hardly progressive teaching, but with these numbers and limitations your first priority has to be to keep them focused or else it will be mayhem.
Good er… make your own luck!