How to verify the accuracy of a pH meter
Your school should have a purchased buffer solutions that have been calibrated against a NIST standard.  If they don't, have them purchase several in order to span the entire pH range, here's one from Sigma-Aldrich.  For your calibration, pick a standard solution that is close to the range you plan to work in.  Here's a couple of links with some more "tips" on how best to actually perform the calibration.


tips #1
tips #2