I don't know where you live or what your exposure has been to tell you anything about the skin test.
A chest xray will tell you if you have the disease and if you do you are contagious. But if start treatment for active disease, you should be fine to start teaching in the fall. (do you have symptoms such as weight loss, cough, night sweats).
If you don't have the disease, the skin test may be indicative of infection, which you should treat with the 9 month course of antibiotics (isoniazid) to prevent actually getting the disease in the future. Its important to take it for 9 months because the TB bacteria is a tough one to kill.
TB isn't that common in the US, but its here. if you are infected your risk of getting the disease is about 30% in your lifetime, but it also depends on other risk factors.
The dr should inform you of your options once the chest xray results come back and he/she knows your exact situation first. But don't worry, there is treatment if you have the disease.
E-mail if you want more info