We present quantitative results from the pilot-year of a large scale Swedish educational project in reading development called LegiLexi, inspired by research within the response to intervention and formative assessment traditions. The vision of the project is that every pupil should reach adequate reading skills at the end of grade 3 in primary school. LegiLexi contains a formative assessment tool and a teacher course, which are linked together. We describe LegiLexi and analyze quantitative effects of the pilot year regarding reading development for pupils in grade 1. The design included three conditions; full access to LegiLexi, access only to the formative assessment tool, and control. Results showed that the group with full access to LegiLexi improved their word decoding and reading comprehension the most. For language comprehension, the formative assessment only group showed the highest improvements. Thus, the features of LegiLexi seem to help enhance critical reading skills. Some changes will be made in the project to strengthen methodological aspects and further facilitate pupils' reading development.