If your homeschooled students is looking for college credit while still in high school, the College Level Examination Program (CLEP) college level test is a great resource. The CLEP is a subject test, which measures one subject at a time, and there are 33 CLEP subjects. Because it's a subject test, it will not meet your state's annual assessment requirements. Many colleges will accept these tests and give credit for them, so check with your individual colleges to see whether they do this.
CLEP test scores range from 20-80; a passing score is anything above 50 for most tests. A college itself will decide what is the acceptable score that is required for them to award college credit. Foreign languages may have a higher testing requirement, such as a 60 or 65 in order to get college credit.
One of the unusual things about the CLEP is that it is computer-based. Other subject tests are taken using paper and pencil at a local high school.
CLEP tests are usually taken in computer labs, usually at a university, vocational college, or community college. Military bases also offer CLEP tests. The College Board lists testing centers located close to you. Because these tests are administered at colleges, they are typically available year-round. Since the test is completed on a computer, your score will be immediately available after you finish the test.
CLEP tests are accumulated by the College Board and sent to whichever colleges you designate in the form of a transcript. The transcript looks identical to a community college or university transcript, so it's very official looking and it's very good outside documentation.
Many public school families have not heard about CLEP, because they're not offered at the high school, but CLEP tests have been around for a long time. Historically, they were offered to adults and college students. Colleges are very used to seeing CLEP tests, as they see their college students take them all the time. Adults can take CLEP tests to satisfy undergraduate requirements and get into college right away.
In order to prepare for the CLEP test, I suggest you use the official study guide. There is a new one available every year, but they don't really change a lot over time, so if you get something that's 3-4 years old, it probably hasn't changed. The study guide will have one assessment test for each subject that is available, which you should use to assess your student. It's important to make sure your student will do well on the test before they take it, so assessing their readiness is very important.