Speaking a foreign language is a useful skill and one that should often be learnt when young. In America, Spanish is considered a practical language to learn, due to the country's border with Mexico and the large segment of the U.S. population that speaks it. Prospective Spanish teachers need to make sure they meet all the necessary requirements in their state before they can start teaching.
The first requirement any Spanish teacher has to meet is education. Spanish teachers at the high school level are required to have at least a bachelors' degree in Spanish. It's also recommended that Spanish students travel abroad and take advantage of any foreign language programs available in Spain or Mexico. Learning the language straight from people who grew up speaking it is a major advantage. It helps prospective Spanish teachers by exposing them to the language as it's spoken in other countries.
Once you've acquired your bachelor's degree and proved that you're relatively fluent in Spanish, you'll need to take a teacher training course. This course is required by your state, and the course requirements are set by the state's licensing board. This can be a short course in how to teach, and it will give the student some teaching experience so he can understand what it's like to be in front of a classroom full of students. Once the course is passed, the teacher has to become licensed and certified.
Depending on where she is teaching, a Spanish teacher has to get a license or certification to be allowed to teach Spanish. The requirements for certification vary by state, so check with your state's education department to find out what is required. There will be tests to show that you can teach, and many states may require you to put in a certain number of supervised teaching hours. Be aware that private schools are under no obligation to require that their teachers be certified. If you were to teach Spanish in a private school, certification would be helpful but not necessary.