Fewer than one in five LGBT primary teachers have come out to colleagues, parents or pupils because of fears for their career prospects.
The overwhelming majority of gay, lesbian, bisexual and transgender teachers think it too risky to declare their sexual orientation or identity, particularly if they don't have a full-time job.
This is despite legislation obliging schools to protect staff from discrimination, which was tightened up in 2015 so that religious-run schools could no longer use ethos as a defence in sexual orientation cases.
A culture of fear also flies in the face of the requirement on schools to teach pupils about inclusivity and to create a positive climate around sexual orientation and identity issues.
The figures emerged in an Irish National Teachers' Organisation (INTO) survey of 2,362 members, North and south.
Nine in 10 (90pc) respondents were heterosexual while one in 10 (10pc) identified as LGBT. Almost one-fifth of respondents were principals.
LGBT teachers in the Republic were more likely to come out, with 18pc declaring their orientation within the school community, compared with 12pc in Northern Ireland. One teacher said it wasn't easy to take the step. "I came out very slowly to only one colleague at a time. It was extremely scary and stressful. Being in the closet causes an extreme amount of discomfort and distress," they said.
Having a permanent contract was a significant influencing factor in opening up, with 43pc reporting a link between job security and a decision to come out in school.
Survey participants expressed concerns about facing bias in interviews if it was known that they were LGBT.
One reported that "there is a lot of prejudice out there. I didn't want to take the risk that one of these people would be sitting on the interview panel".
Among the other findings was the one in three teachers saying that they felt inhibited from referencing LGBT identities in their teaching.
Teachers also reported that derogatory language among staff is "still too prevalent in schools" and that a "don't ask, don't tell" culture was prevalent in some schools as a result of their religious ethos or patronage.
Most LGBT teachers who responded said the role of principal was essential to the creation of an inclusive school, but many felt that principals could be constrained by school managerial authorities.
The survey also touched on the issue of homophobic and transphobic bullying among pupils and it found low levels of awareness among teachers on gender non-conformity and gender transition.
The Department of Education requires teachers to implement strategies to educate about and prevent homophobic and transphobic bullying, but 89pc reported they had not received training.
Teacher Cecelia Gavigan, chair of the INTO LGBT committee, said legislative protection was one thing but "unless the culture changes it doesn't make a difference to the lived experience of teachers".
She said schools needed to be proactive in creating a welcoming culture because otherwise "you don't know and, if you don't know, you won't come out".
INTO general secretary John Boyle said the findings brought into sharp focus the challenges faced by LGBT teachers and the work still to be done to ensure schools were safe and inclusive spaces for all.
He said comprehensive training and support would be essential for all teachers and the INTO "will be to the forefront in demanding the Government delivers on this front".