The objectives of the study were: (1) To construct and develop an instructional package for prevention of narcotic drug problem of lower-secondary students in the expansion opportunity schools in Thailand. (2) To find out the effectiveness of an instructional package for prevention of narcotic drug problem of lower-secondary students in the expansion opportunity schools in Thailand. (3) To find out the differences of narcotic drug mean scores between students taking narcotic drug and not taking narcotic drug. (4) To find out the differences of narcotic drug mean scores between the experimental group and control group.

The hypotheses of the study were: (1) There will be significant differences in narcotic drug mean scores of students between pre-test and post-test phases of experimental group. (2) There will be significant differences in narcotic drug mean scores between students taking narcotic drug and not taking narcotic drug. (3) There will be significant differences in narcotic drug mean scores between the experimental group and control group.

The sample comprised 60 students of class VIII from Ching Mai province of Thailand.

Criterion test and questionnaire were developed by researcher for data collection.

Pre-test post-test experimental design was used by researcher. Treatment was given through the use of instructional package which was developed by researcher. The duration of treatment was two months.   

The data were analyzed with the help of t-ratios. 

The findings of the study were: (1) The instructional package for prevention of narcotic drug problem of lower secondary students in the expansion opportunity schools in Thailand was effective. (2) The instructional package was effective as it could show the significant differences of narcotic drug mean scores between experimental group and control group. (3) There was no significant differences in narcotic drug mean scores between students taking narcotic drugs and not taking narcotic drugs.