The purpose of this study was to explore the lived experiences of Thai primary school students who have studied in an English Program (EP) in a university demonstration school in Thailand. EP is regarded as one of Thailand's educational reform goals that will enhance Thai students' English competency through using English as a tool of instruction for teaching and learning in two core subjects, Science and Maths. The program started in primary level and continued to secondary level. A phenomenological methodology was employed to explore the students' lived experiences (n = 10). Semi-structured interviews, classroom observations and document analysis were used for data collection. The data was analyzed using Moustakas (1994)'s phenomenological analysis steps. The findings revealed the essence of the phenomenon. That is, studying in English Program (EP) entailed nine themes under four dimensions as follows: Academic Dimension; Social Dimension; Emotional Dimension, and Personal Dimension. Some implications are discussed concerning the appropriate EP program policy and the inclusion of the voices of teachers and school administrators. Some limitations are also mentioned.