David Klein:

Problem: Find the slope and y-intercept of the equation 10 = x – 2.5.
Solution: The equation 10 = x – 2.5 is a specific case of the equation y = x – 2.5, which has a slope of 1 and a y-intercept of –2.5.
This problem comes from a 7th grade math quiz that accompanies a widely used textbook series for grades 6 to 8 called Connected Mathematics Program or CMP.[1] The solution appears in the CMP Teacher’s Guide and is supported by a discussion of sample student work.
Richard Askey, a mathematician at the University of Wisconsin at Madison, reported, “I was told about this problem by a parent whose child took this quiz. The marking was exactly as in the text.”[2] Students instructed and graded in this way learn incorrect mathematics, and teachers who know better may be undermined by their less informed peers, armed with the “solution.” This example is far from the only failing of CMP. Among other shortcomings, there is no instruction on division of fractions in the entire three year CMP series, and the other parts of fraction arithmetic are treated poorly.[3]
Is CMP just an anomaly? Unfortunately not. CMP is only one of more than a dozen defective K-12 math programs funded by the National Science Foundation. More specifically, the NSF programs were created and distributed through grants from the Education and Human Resources (EHR) Division within the NSF. In contrast to the NSF’s admirable and important role in supporting fundamental scientific research, the EHR has caused, and continues to cause, damage to K-12 mathematics education.

Notes and links on math curriculum. Audio / Video from the recent math forum.
Connected Math is widely used within the Madison School District resulting in no small amount of supplementing by teachers, students and parents.