ARUNDEL — An arbitrator has told Regional School Unit 21 to stop taking and acting on applications from parents seeking to enroll their children at the Middle School of the Kennebunks.

The order, signed by arbitrator Patrick C. Coughlan, requires the school unit to stop taking applications, stop acting on applications it has already received and to not actually enroll any Arundel students at the middle school until he makes a decision on a contract dispute between the school district and Thornton Academy, a private school.

The dispute revolves around how many Arundel students must be sent to the private academy, which has operated a middle school that primarily caters to students from the town. Arundel, Kennebunk and Kennebunkport schools are part of the RSU and the district believes it would be cheaper to send the students to the middle school in Kennebunk than to pay tuition to Thornton Academy.

The RSU 21 school board has voted to buy out the last five years of the contract with Thornton Academy, beginning next June. Under the state’s school consollidation law, middle school students will still have the option of attending either school once the contract ends.

School officials have said that the parents of 19 children have applied to have their children attend the Middle School of the Kennebunks and said the number reflects substantial interest in the new school choice. Coughlan’s order refers to 17 applications.