The Center on Education Policy released a report titled Choices, Changes, and Challenges: Curriculum and Instruction in the NCLB Era,

The report finds that approximately 62% of school districts increased the amount of time spent in elementary schools on reading/language arts and /or math, while 44% of districts cut time on science, social studies, art and music, physical education, lunch and/or recess.

About 44% of districts reported cutting time from one or more other subjects or activities (social studies, science, art and music, physical education, lunch and/or recess) at the elementary level.

Changes in time assigned were more prevalent in districts with schools identified for
improvement.

Since 2001-02, most districts have changed their English/language arts and math curricula to put greater emphasis on the content and skills covered on the state tests used for NCLB.

The report does not directly address changes in instruction-learning efficiencies.

Tablet PC Education Blog