The UK's biggest union for teachers is telling members to be prepared for increased ethnic tensions between pupils, following the London bombs.
The union is concerned about Muslims in particular
The National Union of Teachers said there had been problems in some areas.
Teachers from minority ethnic groups, particularly Muslims, might also be vulnerable from some pupils and parents, its guidance said.
General secretary Steve Sinnott said open discussion was the best way to counter ignorance and prejudice.
"The terrorists' actions were timed to coincide with workers' and pupils' travelling to offices and schools," he said.
"We are determined that they will not cause division in our schools."
Pupils and teachers must be protected from abuse and threats.
"The best way to deal with such problems is to bring them out in the open, to discuss them and ensure that all involved understand that racism is not acceptable.
"Pupils and teachers must be able to carry on their normal lives free from fear."
He said negative and stereotyped views of Islam and Muslims contributed to prejudice.
Teachers should be especially vigilant for signs of name-calling, abuse and bullying and intervene early to prevent things from escalating.
But the NUT said no attempt should be made to take a politically partisan approach or to belittle a particular set of opinions.