Upon signing on as a tutor, you must take subject tests of your interests. You can be certified in multiple subjects as you wish. Keep in mind though you only have one opportunity to pass. Some tests require at least 60 or 70 or even 80% accuracy to be considered passing. You just have to read what the minimum accuracy percentage is. In my experience, all of the math subjects I certified for have 70% accuracy and grammar with at least 60% accuracy.