The superintendent of Dover and Sherborn’s school systems, Valerie G. Spriggs, knew her assistant, Steven Bliss, was itching for the top job, and she knew he’d be good at it.

But with a year left in her contract, Spriggs also knew that the colleague she worked so well with, and who had a “terrific” relationship with all three school boards in the two-town district, might be tempted to take a job as superintendent in another community rather than wait to see what she would do.