What the school told you seems to be the case according to the California Compulsory Full-Time Education Law (see below for link)
https://law.justia.com/codes/california/2005/edc/48200-48208.html
The California Dept. of Education is required to provide home “individual instruction” to students with temporary disabilities. In order to comply with the Compulsory full time ed requirement - in this situation, one hour of instruction counts as one day of attendance. Then the school is required to allow the student to complete all assignments within a reasonable period of time.
It doesn’t make sense, as how could he reasonably be able to be provided with an adequate education under those policies - one hour/day = one day of attendance?? How could he learn everything in one hour that he would have been taught in a full school day? Seems like this policy is just a way to say a kid is receiving a “full time” education without the benefit of learning anything.
I would definitely contact someone in the school district office to clarify an educational plan for your son. For example, considering his injury and the doctors recommendation, what is the “reasonable amount of time” that he will be allowed to “complete all assignments and tests missed during his absence?” How will he learn all the material in his classes with just one hour of instruction/day? The law says that his teachers will determine the tests and assignments that he’ll be required to make up - so how will that work and on what schedule?
I’d also look into homeschooling (looked at as private schooling under CA laws), which would exempt your son from the one hour/day “individual instruction” requirement of the public school system and would keep him from falling behind. The link below has details about home school policies.
"Homeschooling families have four legal options to homeschool:
Establishing your own home-based private school,
Enrolling in a private school that offers independent study (PSP)
Using a public school independent study program (ISP) or charter school that caters to homeschoolers, or
If you have a credential, using the tutorial option."
http://www.californiahomeschool.net/how-to-homeschool/legal-options/
If he was cleared by your doctor next semester, he could probably make up his credits by homeschooling in the spring and summer and be ready to return to regular school next year and still be on track.
Jeesh, what a ridiculous situation. I hope you get some better information and assistance in developing a plan for your son from the school district.