My son ( 4yrs) teacher at school has tb. everyone only found out 2 weeks ago. my son started coughing last week friday and today has a fever?

Call local officials: TB is a VERY slow growing germ that is hard to pass in a community or school setting. In the US local health authorities track all cases and provide screening tests and advice based on level of contact. Given your time sequence this is likely something else, but you should find out what the local officials advise for all such contacts.