An organizing structure that in recent years has had a major impact on how to work with students who don’t respond to regular instruction is Response to Intervention (RTI). Efforts in RTI are divided into three different tiers of instruction: primary, secondary and tertiary. In our study, we investigate the impact of intensive secondary-tier instruction on students’ knowledge of basic combinations of digits in addition. We also focus on how the students develop their use of more advanced calculations in addition during the intervention.

The results showed that students became faster at performing simple addition tasks, which indicates that their fluency – declarative knowledge – developed during the intervention phase. Our results thereby strengthen suggestions that a secondary-tier intervention level should take place in a small group of students 20-40 minutes four to five times a week. Meanwhile, the students developed their ability to solve two-digit arithmetic tasks in addition and subtraction, which could be explained by the fact that students had automated simple number combinations and thus could focus on the calculation procedure.