Oh, I'll be the first to say that we need better math instruction in schools, from people who understand it themselves. I just find that these studies that start with "there's a correlation between not understanding fractions and not being able to learn algebra" and go directly to "we need to teach fractions better" may be skipping an important logical step. (I haven't read the paper, so I don't know if it's guilty, but the major typo in the abstract you just posted doesn't make me hopeful.) Just because one thing is correlated with another does not mean that there is a causal chain where we can fix the other by fixing the first. It doesn't mean we independently shouldn't fix the first, because it is valuable in its own right. But the problem is that when you start fixing the antecedent, and then you don't get the results you wanted because they weren't actually causally linked in the first place, then the natural response is to stop bothering to fix the antecedent, even though it may have been good and worthwhile for other reasons that you're not paying attention to.