The short answer: probably not.
Texas law assumes that appointing both parents as conservators best serves the child’s interest. Each conservator comes into a Suit Affecting the Parent Child Relationship (SAPCR), which is the fancy term for a custody suit, with assumed rights. Among those rights, every parent can inquire about and attend school activities.
The only way to limit those rights is to get a judicial finding in writing that says the limits are in the child’s best interest. This tough standard can only be met in a court setting and only becomes an issue if one of the litigating parents brings it up and meets the minimum threshold for evidence of risk to the child.
For more information on the list of default parental rights, take a look at the Texas Family Code, Section 153.073. If you want any of those rights limited, make sure you inform your attorney.
If you have a current order in place and it does not explicitly limit the other parent’s right to attend school activities, do not try to limit that access or you could find yourself in trouble. And if you want to add a limitation where one does not exist, contact an attorney to see if you qualify for a modification of your existing order.