The following were the stages of data collection:
The methods of developing the research tools were discussed as follows:
3.3.1 With reference to the pre-test and post-test, they were divided into four main parts with the total of 60 items: part 1for the samples' pronunciation test of vowel sounds with 15 items, part 2 for their pronunciation test of consonant sounds with 15 items, part 3 for their pronunciation test of word stress with 15 items, and part 4 for their pronunciation test of linking sounds with 15 items. After being examined and approved by three experts, each part of the pre-test and post-test would be selected ten items with the total of 40 items for testing 35 samples' English pronunciation skill. The pre-test and post-test of this study was experimental design used for testing the samples in the same target group called"group pretest-posttest design"(Kidrakarn, 2001)
3.3.2 The lesson plans were composed of six sets used as the teaching tools for developing 35 samples' pronunciation skill after testing the capability of their pronunciation with the pre-test Each set was taken in teaching their pronunciation for three hours per week with the total of 18 hours.
According to above-mentioned pre-test and post-test and lessoa plans. all the contents were chosen from three selected English songs: "Let it go"Haven't met you yet", and"As long as you love me all of which were examined and approved by a foreign expert and three Thai experts with both the content validity and the face validity.