Is submitting papers based on classwork papers self-plagiarism?
The problem with typical self-plagiarism is that a scientific work or part of it is published twice in a peer-reviewed venue. This inflates the scientific credit obtained for this work and wastes the times of everybody involved in the publication process.

Assuming that your classwork is not scientifically published (if it is, you should know), you should not commit self-plagiarism. To be on the safe side, I suggest to clearly reveal the history of your paper when submitting. This way, the publisher cannot claim that you hid something from them and they can decide themselves whether they have any problems with it.

Some further remarks:


If your work was published non-scientifically (e.g., hosted on the course’s website), this may conflict with the exclusive copyright wanted by some publishers. However, for most publishers, this should not pose a problem. Be sure to read the copyright-transfer agreement or similar thoroughly in this respect.
Your university may impose some restrictions on publishing coursework. You’ll have to check.
Be aware that whoever supervised your classwork (if anybody) may have contributed to it to such an extent that they deserve authorship. Again, this is something you have to check.