This is pretty standard, as others have mentioned. My middle kid took Honors Biology in 9th and was one of the few recommended for AP Bio in 10th (typically a 12th grade course). However, the school insists you take Chemistry in 10th grade (as well as swimming, which caused some problems too). Since she takes two languages, she couldn't fit two sciences in the schedule.
So kid took Chemistry at a private school over the summer prior to 10th. This was the only approved Chemistry course for our public HS. After the HS got her transcript, they said she needed to take the HS Chemistry final - and she had to take the Honors final - and get an 80%. They would not give her a copy of the HS Chemistry textbook (covered a few different topics than the course she took), wouldn't give her the study guide, and told her it was all multiple choice (not true). She took the final and a few weeks later I got an email that she got a 90%. Then they asked her to do a lab so she could prove she understood things...it is an endless battle.
You are fortunate that the school will let him take the final to place into AP Bio. But multiple AP sciences can be done, as my kid will have AP Bio, AP Physics 1 and AP Physics C by the time she is finished, as well as two languages through AP level.
