This three-year qualitative study examined how district personnel interpreted the Common Core State Standards (CCSS) in English language arts for bilingual teachers' Spanish literacy instruction and the changes that four dual-language (DL) teachers (K-2) made in their Spanish literacy instruction in response to their participation in professional staff development (PSD) on formative assessments tied to the CCSS. Although the district personnel showed ideological and political clarity when they implemented a DL program and rejected CCSS inappropriate for bilingual students, they showed a lack of clarity when they failed to provide Spanish literacy and DL standards. In response to the socio-culturally oriented PSD, two of the DL teachers, who previously had taught Spanish reading, effectively implemented formative assessments, which led to teacher and student goal setting and sharing, student self-assessment, peer assessment, and instructional differentiation. However, it took two-three years, scaffolded support, and teacher sharing and collaboration for them to implement the formative assessments. The lack of Spanish literacy and DL standards meant that other changes in their Spanish literacy instruction were limited. In response to the PSD, the veteran kindergarten teacher made a change in her writing instruction, but never understood formative assessments and didn't implement them. The learning curve for the teacher without teaching experience in Spanish reading was too steep for her to benefit from the PSD on formative assessments. To improve DL teachers' Spanish literacy instruction, the development and implementation of Spanish language arts and DL standards, along with socio-cultural PSD on formative assessments, were recommended.