Please dont issue legal notice, please follow the administrative process. put in presentation either verbal or written to your superior. issue of notice means you have challanged the dept., in that situation they have to defend your notice.
The remedy of writ is likely to be expensive.Since you are teacher, you can take up the matter with education Dept. of the state.Since administrative remedies are available,there is chance of writ being not admitted. So first persue administrative solution and if you are not happy with decision of the department, you can file writ petitionand chances of writ being admitted would be good.