How to put an iPhone 4 on silent with no vibrate?

In my history class, the teacher has us turn off our phones and put them in his box so we aren't tempted to text in class. I don't want to do this because I'm afraid someone will steal my phone, so I'm wondering how to put my phone on silent where it doesn't even vibrate so if it is in my bag, he won't know.

In settings select vibrate - off. Use the silent button next to the volume controls to turn off all sounds.

Unfortunately, that is impossible to put an iPhone 4 on Silent with no vibrate.

Settings>sounds>turn off vibrate on silent

You could use Do Not Disturb to do that.