With the rapid development of artificial intelligence in many disciplines, computational thinking (CT) has become an important skill for the 21st century. To promote vocational high school students' CT skills in learning about programmable logic controllers, this study intended to examine how cognitive and metacognitive prompts separately or together influenced students' development of CT. The findings revealed that metacognitive prompts significantly improved students' CT outcomes, self-efficacy, and motivation for learning. The study offers important implications regarding the strategies to promote CT in vocational high schools.