Trpt. allowance-recd nil-claimed 19200 employer obligation

Yes, correct.....

Then, it  may  mean the employee cannot claim while filing the return also.

If that school head argument is correct - what about exemption of exemption of preventive medical check up exemptin of 5000.

Is that also not allowed OR to be claimed only while filing the return.

How many employers give any amount for preventive check up. 

------can they disallow this also as they are not disbursing any amount  under the head of preventive health check up.

 agains doesn't it mean the school is disallowing which law allows to claim..!!!

Section 80D is separate deduction under chapter VI A, not anyway connected with employer.

Allowance like transportation, medical etc. are paid extra by employer. If it is paid it can be claimed u/s. 10; otherwise cannot be claimed.