Based on a report: Taking science to school: Learning and teaching science in grades K-8 by the Committee on Science Learning, Kindergarten Through Eighth Grade, students need to acquire specific knowledge and skills, participate in certain practices and become fluent in them to be considered proficient in science.
The report says:
“Students who are proficient in science:
1. know, use, and interpret scientific explanations of the natural world;
2. generate and evaluate scientific evidence and explanations;
3. understand the nature and development of scientific knowledge; and
4. participate productively in scientific practices and discourse.”
It then continues saying that these strands of scientific proficiency are not independent of each other. They’re intertwined. The report explains each one in detail and provides recommendations of how to improve science education in grades K-8.