- Spousal / partner visa. If you're married to / in a relationship with a national, you'll probably get granted a visa. Some countries allow you to work on this visa, others require you to get permission to do so. Check beforehand.
- Dependent visa. If you're married to / in a relationship with someone with a visa, you may be able to work. Such is the case with Japan. Its neighbour, Korea, has different rules though. It's illegal to work or even study on a dependent visa.
- Working for someone else. If you have a visa with ABC school and decide to do part-time work at XYZ school, you're probably breaking visa rules.
- Working on a business visa. Business visas are usually for those who do short-term (i.e., less than 6 months business in that country). If you're there longer, you're working illegally.
- Teaching private lessons. Korea's famous for this. Teaching private lessons is a big no-no. That's not to say that it's not common for teachers to do this. Don't get caught though or you'll get slapped with a heavy fine or even deported.
- Teaching on a tourist visa. In many countries in Latin America or Southeast Asia, teachers may teach on a tourist visa. Be aware that in any country earning money on a tourist visa is illegal, even if you do it for a short time. Often these teachers only stay for a short time, or the visa laws are lax so they can border hop and just come back in a day or two later. Nonetheless, it's still illegal.
- Getting a work visa illegally. Some countries have requirements for teaching experience, such as China. In some provinces you're required to have two years teaching experience in order to get a visa. China being China, it seems to be who you know and who owes who what favour that can get you out of this requirement. It's not unheard of for bosses to fudge teachers' CVs or for the immigration officers to grant your boss a favour if you don't have the required experience.
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