It usually depends if the counseling is court ordered. I'm guessing it is in this situation because you are on probation. I'm almost positive they would tell your PO if you failed a UA. I'm on felony probation and if I fail a drug test at my outpatient treatment center they fax the results to my PO; whether it's positive or negative.

And also, I'm pretty sure your drug counselor would find it suspicious if you missed a week of school. Even if he/she didn't they're probably going to UA you the next chance they get. But it could buy you some time. Good luck homie.