So, what is the law anyway?

Massachusetts  General Law  CHAPTER 90

Section 14: Precautions for safety of other travelers

“When approaching a vehicle which displays a sign bearing the words ''SCHOOL BUS'' and which is equipped with front and rear alternating flashing red signal lamps which are flashing, as provided in section seven B, and which has been stopped to allow pupils to alight from or board the same, a person operating a motor vehicle or trackless trolley shall, except when approaching from the opposite direction on a divided highway, bring his vehicle or trackless trolley to a full stop before reaching said school bus and shall not thereafter proceed until the warning signals are deactivated, unless directed to the contrary by a police officer duly authorized to control the movement of traffic. 

 Any person who violates the preceding sentence shall be punished by a fine of not less than $250; and for a second offense by a fine of not less than $500 nor more than $1,000; and for a third or subsequent offense by a fine of not less than $1,000 nor more than $2,000. A second conviction or third or subsequent conviction as set forth in the preceding sentence shall be reported forthwith by the court or magistrate to the registrar who shall revoke immediately the license or right to operate of the person so convicted and no appeal, motion for a new trial or exceptions, shall operate to stay the revocation of the license or right to operate; provided, however, that no license or right to operate shall be issued by the registrar to any person convicted of a second such offense until 6 months after the date of revocation following said conviction or to any person convicted of a third or subsequent such offense until 1 year after the date of revocation following said conviction; and provided, further, that if the prosecution against such person has terminated in his favor the registrar shall forthwith reinstate his license or right to operate."