A health exchange’s first task is ensuring that those who are eligible for benefits know about them — right now, research suggests three-quarters have no idea.

That suggests a huge outreach challenge — and one the federal government may not be ideally suited to completing. Evidence suggests that it works better when it caters to local markets. Massachusetts, for example, saw high enrollment after it partnered with the Red Sox to promote its health-insurance exchange.

After people become aware of benefits, the health exchange faces its biggest challenge: Figuring out who is eligible for what. In many states those who earn less than 133 percent of the Federal Poverty Line are eligible for Medicaid — except if the state has already extended benefits to an even higher level, as 35 states have for children…

An old Medicaid system, for example, may only have the capacity to send large batches of data each night. That was fine back in the 1980s, when most applications happened by mail. It’s less desirable when you have a law that would like to see real-time application processing.