For Father’s Day, Paul Rimmer headed to a service at the centuries-old Gothic chapel that he liked to visit in Cambridge, England, this time bringing his son, Tristan, 9, with him.

Tristan was enjoying the service — staring at the ceiling in awe, laughing happily — when an usher approached. The boy was being disruptive, the usher said, and needed to leave.

When Mr. Rimmer explained that his son, who is autistic, was expressing his excitement by laughing and calling out, the usher was apologetic but unmoved.

After leaving, Mr. Rimmer sent a letter to the chapel’s leadership and posted it on Facebook, setting off a reaction that drew a public apology from the dean of chapel at King’s College, Cambridge, and an outpouring of support from families who had also felt discriminated against or stigmatized because of autism.