I think you might be making the mistake of projecting your own real-world observations and assumptions onto the argument.

When you have a STRENGTHEN question, the first step is to ask yourself - what is the argument missing? Are there any assumptions or logical gaps to address?

In this argument, the author is concluding that students will not succeed in designing their own curricula because they lack maturity and experience. Thus, the author is assuming that maturity and experience are the necessary conditions for success: good curricula = maturity + experience.

If we want to strengthen this argument, we need to add in a new piece of information that supports this idea. We don't have to make the conclusion 100% true, we just have to support that underlying assumption. You might be perfectly correct that in the real world, going to school for 10+ years would give students "familiarity with educational life." Your job isn't to find what's true in the real world, though. Your job is to find the piece of information that - if true - would support that conclusion.

I agree that it's a bit of an annoying answer, but that will sometimes happen on the GMAT! Does it make sense why that's the only answer choice that speaks to our assumption, though?

I believe that this is the same question:

The local high school students have been clamoring for the freedom do design their own curricula. Allowing this would be as allowing three-year-olds to choose their own diets. These students have neither the maturity nor the experience to equal that of the professional educators now doing the job.

Which of the following statements, if true, would most strengthen the above argument?

A. high school students have less formal education than those who currently design the curricula.
B. Three-year-olds do not, if left to their own devices, choose healthful diets.
C. The local high school students are less intelligent than the average teenager.
D. Individualized curricula are more beneficial to high school students than are the standard curricula, which are rigid and unresponsive to their particular strengths and weaknesses.
E. The ability to design good curricula develops only after years of familiarity with educational life.