The introduction of standards into the education system poses numerous challenges and difficulties. As with any change, plans should be made for teachers to understand and implement the standards. This study examined science teachers' perceptions of the effectiveness of the standards for teaching and learning, and the extent and ease/difficulty of implementing science standards in different grades. The research used a mixed methods approach, combining qualitative and quantitative research methods. The research tools were questionnaires that were administered to elementary school science teachers. The majority of the teachers perceived the standards in science as effective for teaching and learning and only a small minority viewed them as restricting their pedagogical autonomy. Differences were found in the extent of implementation of the different standards and between different grades. The teachers perceived a different degree of difficulty in the implementation of the different standards. The standards experienced as easiest to implement were in the field of biology and materials, whereas the standards in earth sciences and the universe and technology were most difficult to implement, and are also those evaluated by the teachers as being implemented to the least extent. Exposure of teachers' perceptions on the effectiveness of standards and the implementation of the standards may aid policymakers in future planning of teachers' professional development for the implementation of standards.