A total of 1,689 out of 2,139 students randomly selected for drug tests had taken the tests in the government trial test scheme for Tai Po schools since it was started in December and no positive cases were found. Six students who were selected to be tested refused to take the voluntary test. Two false-positive cases were found in the period. Over 12,400 students had joined the scheme as of yesterday. The trial finishes at the end of the school year in summer.