My ex husband and I have joint custody but I have primary. We disagree on homeschooling my ASD son. Can I just pull him out of school?

You DONT have a "joint custody" arrangement with your ex. You have a "joint legal custody" arrangement with you designated as the primary custodial parent. It may not seem like a big difference but legally, the difference should be huge. If you look at the wording of your agreement as to your custody plan, it will say say that you and he will maintain a joint legal custody plan with you designated as the primary custodial parent and then the language of your agreement should define the decision making on "major decisions" affecting your son's health, education and general welfare. Since you are the primary custodial parent, ithe language of your agreement should say that you and he shall "discuss" those type of issues and / or that he shall be "consulted" but presumably, the language of the agreement does not say that each of you shall have an equal say in the decision making process or that neither of you shall act unilaterally in the decision making or that in the event of a disagreement, you and he shall submit the issue to a mediator or to the court.   If the langauge of your agreement does say that you and he shall have equal say in the decision making process or that neither shall act unilaterally or that in the event of a disagreement on how to handle a major decision, you and he shall submit the issue to mediaton or to the court, then its a little more complicated and I would therefore send him an email or a text message laying out what you want to do and your reasoning for it. Spend time to lay out all of your reasons since you may need that email or text if you and he end up in court. That message is critical and needs to be addressed to him in complete thoughts so that if a judge is reading it, you make sense and your reasoning is logical.  If he does not respond, make sure to also print out that message so that if he later claims that he never got the message, you have proof that you sent it to him.