Praise be to Allah.
Your saying “I swear an oath …” is not a clear statement of divorce; rather it is a kind of metaphor, so it depends on your intention:
1.If your intention was to encourage her to go to school and prevent her from missing classes, and you did not intend to divorce her if she refused to go, then she is not divorced if she misses classes, but you have to offer expiation for breaking an oath.
2.If you did intend divorce in this case, i.e., that she would be divorced if she did not go, then she is divorced if she did not go.
3.If she went then skipped class, this also depends on your intention. If what you meant was that she should never skip class, then it counts as a divorce; but if you meant that she should go and not refuse, and it never occurred to you that she would skip class after going, then no divorce has taken place if she missed classes.
4.If divorce has taken place, then it counts as one talaaq.
Divorce in the case of anger is subject to further discussion, as has been explained previously in the answer to question no. 22034
The number of divorces depends on the details discussed above.
But we should point out that even if divorce has taken place, then the talaaq is repeated during the ‘iddah, before taking the wife back following the first divorce, then only one divorce has taken place according to the more correct scholarly view.
See the answer to question no. 126549
We should also point out the importance of refraining from using the words of divorce (talaaq), so as to protect your household and family.
And Allah knows best.