Can I claim tax back on extra expenses related to my job?

Say I am a teacher. A lot of teachers use their after-tax salary to pay for paper, pens, printing (etc) for school purposes. Is there a way to claim tax back since it is a work expense?
In this case, the school does not refund the money.

Is your teacher's salary your only income?

Yes, it is.

Unfortunately, you won't be able to claim this expenditure as a deduction. There are limited expense deductions allowable for salaried employees.
It would be best to motivate for the school to reimburse you for these purchases.