Some are a bit tricky, though. The student is using logic, and deductive reasoning, to solve a problem, rather than just formally doing a proof. The following statements are not intended to discredit SM or any other program that does not teach proofs directly. I only mean to offer an opinion that may be different from current popular math teaching ideology. I am afraid that I would have to disagree that the practice of writing a formal proof is unimportant to learning to reason through a problem.
Proofs also teach the discipline of having a supporting reason for every statement.
Those students who are struggling because they haven't fully reached the formal logic stage of cognitive ability are the very ones who need the practice proof-writing provides. A geometric proof is the concrete practice of an abstract thought process. Years later they may not be able to quote the postulates verbatum, but they will demonstrate the same logical sequencing in solving problems that they practiced in Geometry. I don't doubt that one can learn reasoning and geometry in a number of different ways, but it is often to the student's disadvantage to abandon the more challenging path. I am using NEM 1, doing geometry.