Interesting results out from the followup to the 1998 Rudner study on the standardized test scores of homeschooled students. Homeschoolers scored nearly 40 percentage points above their government-run school counterparts on the Reading subtest and 34 percentage points above on the math subtest. Results did not vary signficantly by gender, family income, amount of money spent on homeschooling curricula, whether the parent held a state teacher's credential, or the level of government regulation required by the particular state. The education level of the parents did affect the results; however even when neither parent had a college degree the kids still scored in the 83rd percentile, well above the comparable results for government-run school kids.
Our family did not participate in this particular study as we've not yet had my oldest take a standardized test (she's only 6).