They could call the doctor to confirm the certificate.but the teachers have nothing to do but attribute ultimate legitimacy to it, so they can't say anything.
Oh, yes, but I'm saying some doctors could leniently give it out. It happens all the time. So yeah they'll confirm the certificate, but that doesn't mean the certificate is 'authentic' (i.e. that the kid was actually sick).They could call the doctor to confirm the certificate.