(As a current 6th grader, she is in Honors Algebra.)
Is this a normal option for 6th graders or is this because of outside testing? Here, where 9th grade algebra is the norm, it would be very unusual to allow this.
The full answer to that question is a long one, but the 6th grade algebra placement had everything to do with internal testing/acceleration on the part of the district, and nothing (or little) to do with outside testing. Our neighborhood middle school offers one section (25 kids?) of Honors Algebra that has only 6th and 7th graders- but it may be the only public school in our state to do so. And the class is taught by a teacher with an MS in Math, another rarity.
Here's how our kids ended up in Algebra in 6th grade. Historically, our district has given 5th graders a math test for placement in 6th. In 4th grade, our kids (twins) were invited by the district to take this test, without any real explanation of why - but we said yes. It turns out the test is also used as a qualifier for a district wide math pull out for 5th graders. Our kids' 3-5 school is a differentiation-R-us, pullouts-R-bad kind of school, so when they heard we were considering signing the kids up for the pullout (dd had the district-wide high score on the qualifier), they (principal/teacher) went through the roof.
After tense discussions a compromise was reached -- the kids WOULD be taught the curriculum used in the pullout, except that they would receive the curriculum from their classroom teacher in 5th grade and would NOT attend the pullout. As a result, when the actual 6th grade placement process came around at the end of 5th, they wound up with a placement in Algebra.