The present study aimed to examine the effect of collaborative practices among teachers on student achievement in state-tested science courses. Using an action research model, the author planned, implemented, and evaluated the effect of teachers collaborating in PLCs in science classes in a rural school district. Prior to the study, teachers in the district reported that they had never had the opportunity to collaborate with other teachers at different schools in the district. The school and district leaders had previously made attempts to form PLCs, but they were unsuccessful in their efforts. The district coordinator used vertical and horizontal alignment meetings throughout the school year to support the teachers' needs. Findings of the research show there was a 14% increase in students testing on the proficient and distinguished levels on the End of Course Assessment in 8th grade science, an 11% increase in Biology, and a 3% increase in 5th grade science after less than one year of the collaborative practices.