Despite the increasing popularity of dual language education programs in Taiwan, limited research assesses their effectiveness. This study evaluated eight English Immersion Programs (EIPs) in Taiwan, representing a dual language education model, using the "Guiding Principles for Dual Language Education" (GPDLE) framework. Interviews with the management team and a questionnaire for Native English Teachers (NETs) assessed the alignment of program structure and instruction with the GPDLE. A quasi-experimental design, including pre-tests and post-tests, examined the English listening and reading outcomes of 74 fourth to sixth-grade students in two randomly-selected EIPs over a year. The findings reveal that 83% of the EIPs fully adhered to the program structure outlined in the GPDLE, while only 33% of teacher instruction exhibited full alignment, with an additional 57% demonstrating partial alignment. Notably, significant improvements in reading were observed among fourth-grade students, and both reading and listening skills showed substantial enhancements in the fifth and sixth-grade students. The study recommends adopting a financially sustainable, user-paid model for an after-school English immersion program, supporting Taiwan's 2030 Bilingual National Initiative.