This study examined six reading intervention teachers' implementation of the SPELL-Links to Reading and Writing intervention with students in Grades 2 and 3. The purpose was to explore the extent to which teachers who received a one-day training session without ongoing coaching support were able to implement the intervention with fidelity. It also aimed to better understand the determinants (i.e., barriers and facilitators) of teachers' implementation and their perceptions related to the importance, feasibility, and effectiveness of the intervention. Data from four sources (implementation logs, implementation observations, interviews, and surveys) were collected and analyzed. Participating teachers did not implement the intervention at the intended dosage of 4 days per week, but they did demonstrate high adherence and quality on average. Several barriers to implementation were identified, including intervention training, intervention content and structure, compatibility with existing practices, and alignment with goals. Notable facilitators of implementation were teacher capability and peer support. Teachers had varying perceptions of the intervention, with neutral satisfaction on average. These findings indicate a need for further research on determinants of intervention implementation as they may be crucial in supporting teachers' implementation fidelity.