Most of the Affordable Care Act won’t take effect for a few years — and if court rulings and the 2012 elections go a certain way, it may not take effect at all — but there’s already evidence that the reform law is working.

The Center on Budget and Policy Priorities’ Bob Greenstein, for example, scrutinized the latest Census Bureau data yesterday, and noticed that as poverty gets worse, the number of Americans without health insurance continues to climb. But there’s a silver lining:

[T]he new data suggest that the health reform law may already be having a positive effect on coverage; the requirement that health insurers cover adult dependent children up to age 26 likely contributed to the significant reduction in the number and percentage of young adults age 19-25 without health insurance between 2009 and 2010. This is the only age group of non-elderly adults for which the percentage without insurance declined between 2009 and 2010.

This is no small development. As economic conditions remain weak, more and more Americans are losing health care coverage, but for one group of people — young adults between 19 and 25 — access is suddenly improving. Coverage got worse for everyone, but got better for these younger Americans.

The direct cause is unclear, but it certainly appears that this shift isn’t a coincidence. The Affordable Care Act, over Republican objections, mandates that young adults can stay on their family plans until their 26th birthday. It’s one of the key measures that took effect almost immediately, and as the Census Bureau’s report strongly suggests, it’s already having a positive effect.

For most reasonable people, this is pretty terrific news.

What’s more, let’s also not forget that this isn’t the first sign of Affordable Care Act efficacy. A few weeks ago, we learned that the health care reform law is also having a positive impact on slowing the growth in Medicare spending — a priority Republicans pretend to care about — as hospitals transition to a greater focus on value and efficiency, required under the ACA.

And just yesterday, CBO Director Doug Elmendorf agreed that new law is slowing down Medicare costs, and went on to explain to lawmakers that reform won’t cause private employers to drop coverage for its employees once implemented.

I know the right doesn’t want to hear this, but all available evidence suggests the Affordable Care Act is already working.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.