This is a very common question I run across. St Tammany Parish, including the Cities of Mandeville, Covington, and Slidell, Louisiana, have some of the best schools in the State. Due to this fact, the St Tammany Parish School Board has a handy feature online, through which you type in an address and Bam!, the 4 public schools servicing the address are returned. This is the link for the St Tammany School Board Address Query.
The query will return the Elementary, Middle, Jr High, and High Schools. The School Board is still updating the database, so not every address will work, but they are working to get it complete.
Hope this gets some good use.
Mauti Meredith Scoggin GMAC