Learning to read and spell constitutes a major societal concern. As a result, different studies have been conducted to evaluate the effectiveness of different instructional methods. However, few studies have investigated how teachers appropriate and implement a newly reading and spelling instructional method in the classroom. In order to grasp information regarding this appropriation and implementation, we set up a qualitative study. An online questionnaire was completed by 116 teachers and an interview was conducted with 15 other teachers who voluntarily used a reading and spelling instructional method that they had never used before. A thematic content analysis and the QDA Miner Lite software (ProvalisResearch) were used to analyze the data. The results showed that the conditions underlying appropriation can be organized into three categories: (1) "Context" with the teacher profile, the class profile, and the organizational context, (2) "Implementation conditions" with the resources and time allocated to the implementation of the instructional method and training and supervision conditions, and (3) "Cognitive and Behavioral Appropriation" with characteristics of the instructional method and the knowledge/understanding of the theoretical underpinnings. We thus provide recommendations aiming at improving appropriation of instructional methods, and we highlight methodological challenges for planning effective assessments.