The Milpitas Unified School District made a strategic decision last year to get ready for Common Core. Teachers began the shift toward Common Core, so likewise, students started to shift away from API mode of thinking, thus nobody should be surprised with the drop in API.
The new Common Core instruction is very different from the old API instruction. The old API instruction consisted of simple bubble test questions. With the new Common Core, students need to think and problem solve. The questions are going to involve more open-ended problem solving. Kids still need to come up with an answer, but now they will show their work, which you don't do with a bubble test. The new online assessments will capture the "scratch" paperwork.