HELP ME ADVISE ON MY SON'S PROB?

MY ELDEST SON IS 17 RS OLD THIS YR. HE IS DOING HIS 1ST YEAR IN PETROCHEMICAL COURSE FROM THIS YEAR JANUARY. SINCE HE STARTED ION JANUARY HE SHOWED INTEREST NOW HIS ATTENDANCE IS BAD AND DOESNT DO HIS IGNEMENTS OR DOES HIS CLWORK PROPERLY, AS A RESULT THE SCHOOL HAS INFORMED US OF HIS BAD ATTENDANCE AND IF HE CONTNUES THIS HE WILL NOT BE ABLE TO SIT FOR EXAMS. WE ALSO FOUND OUT THAT HE IS SMOKING AND WHEN I CONFRONT HIM HE DENIES. I AM EXTREMLY WORRIED OF HIS FUTURE AS I ALSO THINKING OF GETTING INTO ARMY FOR ENLISTMENTS WHICH EXIST IN SINGAPORE. OR WHAT CAN I DO?? I AM LOST BUT NOT WNAT TO GIVE UP ON HIM.. PLS ADVISE