I've used the vouchers through the NASN that they offer with your membership..it is a good program. I have also used my local Lion's Club who has a program for kids who need glasses. This year my area had a local "round up" type event free to the public (qualify based on income) where any kid could get an eye exam and fitted for glasses. My school took a bus load of 12 kids and many of their parents accompanying them. 9 were glassed, 2 did not need glasses at this time, and one will be having surgery to correct a serious problem and after recovery from that she will be glassed.
i got a student new specs through new eyes for the needy. Didn't cover an eye exam, but was a fast turn around in getting the voucher. also got a letter from a local pearle vision center with discounted prices on glasses for students and staff. Perhaps if you contact a local pearle they have a similar program.
Not free, but these sites may be an option for parents who don't have insurance but also don't qualify for income-based aid programs (online glasses purchased after obtaining prescription from license optometrist/ophthalmologist):