The class has begun!

Class begins at 10am. This is information to share with the class. A statement. If someone walks in at 10:01, I will tell them class begins at 10am exactly. No problem with this sentence in that particular situation. If you want to start the class, you can either be polite or very direct. The important thing to note is that you're using "class" as a name for the people sitting front of you. So you should probably use a comma: "class, begin" But, yes, it's not very usual to talk like this. And the problem is that students can't begin the class, because the teacher leads the activity. If you were the boss, telling a teacher to do his job, you might say "begin the class," or "start the class." And you could put his name or title before this order: "Teacher, begins the class." If you're talking to students and want to be direct, you might say something like one of these: - Class, open your books. - OK everybody, pay attention. (The class is beginning.) - Class, be quiet and look this way. See? Name, followed by an order. (The imperative form of the verb.) If you are a teacher and want to bring the class to order, there are more polite ways of doing it. It depends on your relationship with the students. - Good morning, everyone. It's time to begin. - Class! Let's begin. Page 20 in your books, please. - OK, class, we are beginning with a video this morning. Personally, I use a more low-key approach: - Are we ready? - Is everybody here? Which page are we on? - Did everyone do their homework? How was it? - Hi, all. How was your weekend? ... OK, let's do something useful now. And so no. It all depends what message you want to communicate, and that depends who the students are and what you need them to do. For a teacher, the important thing is that you're the boss. You can communicate that with clear strong language, or you can use non-verbal communication to take a more subtle control of the class.

Class Begin

They would say class begin. For example, if they were using the word Class to get everyone's attention, and then telling them to begin. For begins, you might say "Class begins at 8 o'clock".

Unless they were waiting for a command to start a task they already knew they were doing, such as waiting for the command to start a test.