The purposes of this research were 1) To study efficiency of science learning in bilingual by using inquiry-based teaching in 5 steps (5Es) technique combined with content and language integrated learning (CLIL) technique. With the topic; “Pure Substances” for the secondary 1 students. 2) To compare science learning pre-learning and post-learning achievements under science learning in bilingual by using inquiry-based teaching in 5 steps (5Es) technique combined with content and language integrated learning (CLIL) technique. With the topic; “Pure Substances” for the secondary 1 students. 3) To study the students’ attitude with science learning in bilingual by using inquiry-based teaching in 5 steps (5Es) technique combined with Content and Language Integrated Learning (CLIL) technique. With the topic;“Pure Substance” for the secondary 1 students. The research population is consists of 18 students studying in Secondary 1, Mini English Program. The study was conducted during the 1st semester of academic year 2019 at Tedsaban 1 (Thungphabodrajbumrung) school under the supervision of Banklang Municipality, Sanpatong, Chiangmai. There were 21 hours of assessment time. The instruments used in this research were lesson plans, a science learning achievement test and a questionnaire on student’s attitude of science learning in bilingual by using inquiry-based teaching in 5 steps (5Es) technique combined with content and language integrated learning (CLIL) technique. With the topic; “Pure Substances” for the secondary 1 students. Statistics employed for data analysis were the content validity by using index of items by the experts. Analyzed the efficiency of science learning in bilingual by using inquiry-based teaching in 5 steps (5Es) technique combined with content and language integrated learning (CLIL) technique. With the topic “Pure Substances” for the secondary 1 students by using E1/E2 technique. Examined the questionnaire’s reliability by using Cronbach’s Alpha Coefficient method. The difficulty of “Pure Substances” science learning achievement test was calculated by Chung Teh Fan technique. As well as, the “Pure Substances” science learning achievement test reliability by KR-20. Comparing pre-learning and post-learning achievements by t-test method. Finally, studied the students’ attitude with science learning in bilingual by using inquiry-based teaching in 5 steps (5Es) technique combined with content and language integrated learning (CLIL) technique. With the topic; “Pure Substances” for the secondary 1 students by using mean () and standard deviation () statistics. The results were found that;

1. The efficiency of science learning in bilingual by using inquiry-based teaching in 5 steps (5Es) technique combined with content and language integrated learning (CLIL) technique. With the topic of “Pure Substances” for the secondary 1 students is 84.60/86.85.

2. The science learning achievements by using inquiry-based teaching in 5 steps (5Es) technique combined with content and language integrated learning (CLIL) technique. With the topic “Pure Substances” for the secondary 1 students was significantly higher than their pre-learning counterpart achievement at the .05 level.

3. The students’ attitude with science learning in bilingual by using inquiry-based teaching in 5 steps (5Es) technique combined with content and language integrated learning (CLIL) technique. With the topic “Pure Substances” for the secondary 1 students was at the highest level. The average and the standard deviation was 4.59 and 0.50, respectively.

Key words: Science Learning in Bilingual, Teaching Science in English, Inquiry-Based Teaching in Science, Content and Language Integrated Learning, CLIL, Pure Substances.

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