Preliminary findings from a real research study, now under peer review:
When comparing these [voucher] students' achievement after the switch to their test scores the previous year, the researchers found:
Voucher students experienced "modest annual achievement losses" in math, especially in the first two years after leaving public school.
In English/language arts (ELA), voucher students showed no benefits.
These results echo what other researchers have found: that voucher students often backslide academically after switching to private school.