Cal. Ed. Code § 87424
If the employee from the district within the state who serves as an exchange instructor without the state and the governing board regularly employing him or her so agree, the district may pay his or her regular salary, making all deductions provided by law for retirement purposes, during the period of the exchange teaching. In such case, the district shall not pay the salary of the exchange employee from without the state, serving the district in exchange for its regular instructor.
In the event an employee from a district within this state serving as an exchange instructor without the state and to whom the governing board of such district is paying the regular salary of such instructor as herein provided, is compelled to absent himself or herself from his or her duties because of injury, illness, or quarantine, the governing board of the district within this state may pay the substitute employed to take the place of such instructor and shall deduct the amount so paid the substitute from the compensation of the employee.
Ca. Educ. Code § 87424