There are three teachers. You get one chance to choose which one you want. When you open the [!] that takes you to school for the first time, the turtle teacher will appear. If you press the A (left) button he will go away and a different teacher will appear. You can press the A button again if you want to select another different teacher. Press the B (middle) button when you see the teacher you want. Or, if you don't press any buttons for a little while, whichever teacher is on the screen is selected to be yours. Once the selection is made, you can't change it.