New guidance will be issued to Bridlington schools after they were targeted by hoax emails.
Bay Primary School and Bridlington Children's Centre closed this morning, while Headlands School received its second threatening message in the space of a month but stayed open.
Several other schools around the East Riding were also targeted and sent pupils home.
A spokesman for East Riding of Yorkshire Council said: "A number of our schools took the decision to close today after receiving this threat, which was an understandable decision given that the health and safety of children is always their paramount concern.
"We will be issuing new guidance to schools in the light of these new and worrying threats."