ZX-81 has released a port of the TI-92 calculator to the PSP. You will need to acquire a ROM of the TI- 92 or TI- 92 plus on your own, and in conjunction with this emulator, you can have a full-fledge graphing calculator on your PSP. How's that for finding an appropiate reason to bring your PSP to school! The entire project is based on GPL'd code, so sources are included for developers to tinker with.
Download PSPXTI TI-92 Emulator v1.0.1 from PSP 3D
here.