I teach 4th grade and have 24. We don’t have any other classrooms, so there isn’t another solution. I do have an aid.
What I have done:
I had the students take the books home, and leave them there. They get “homework” every week to read the next chapter. That gives me time to do the activities in the classroom.
I assigned seats, something I never do. But that keeps the talkers away from the other talkers so that most are listening and learning. With so many in class, you need of the time given to you. You don’t want to have to waste it having to spend telling people to listen.
When learning about the Bible, Divine Revelation and such. I had them learn to look up things in the Bible. I would say, something like John 3-16 and have them find it. One would then read the title of the verse.
Write a word vertically on the board. Maybe something like BIBLE. Then have them use each letter to write something they know about the word. I did it so the letter of the word could be anywhere in the “something they know.” ex: divine reveLation for the letter L of Bible.
Students this age love to tell you what they know. Since they have read the chapter, each child should know something. Ex: “Tell me about Lent.” I got answers like, 40 days, Father wears purple, Ash Wednesday, and so on. Then I expanded on it.
Feel free to PM (private message) me if you want more ideas for specific topics.)