ORS § 328.015
On the first Monday in December the executive officer of the administrative office for the county shall apportion the county school fund among the several districts in the county, in proportion to the resident average daily membership for the preceding fiscal year in each district as reported by the district to the administrative office of the county. In the case of a joint school district, the resident average daily membership reported to the administrative office of the counties comprising the district shall be prorated between the counties as the resident enrollment of the district is prorated between the counties. Any balance accruing to the fund after the December apportionment shall be apportioned in the same manner at such other times during the year as the executive officer of the administrative office may consider advisable.
ORS 328.015