Many young students with Swedish as their second language need support to acquire reading ability. There is a need for evidence-based reading instruction in early reading education for students with Swedish as their first or second language. Therefore, the current study investigated whether early reading education based on a Response to Intervention (RTI) model with a focus on decoding skills can promote reading ability among young students with Swedish as their first or second language. In Grades 1 and 2, 113 students with Swedish as a first and Swedish as a second language were followed. Applying the RTI model, teachers used evidence-based reading instruction in the whole class. Besides, additional instructions were provided in small groups and individually for students with weak decoding. Results of the study showed that the additional instruction provided within the RTI model had the potential to promote decoding, but to a different extent among students with Swedish as their second language. The importance of differentiated instruction, early monitoring and support, a bilingual approach in reading education for second language students, and collaboration between teachers are discussed.