Around 85 percent of respondents to a PTU survey of 586 primary and secondary school teachers said they had used RTHK programmes as teaching material in lessons.
They said the programmes could assist their teaching, as they covered various topics, including current affairs, environmental issues, social problems and history.
A majority of respondents to the survey said allowing students to watch the shows during lessons helped to foster their interests.
They also said they had encountered difficulties in preparing learning materials now that the programmes had been deleted.
The union said RTHK programmes are a high-quality public resource, and the government station should make them available again.
The government broadcaster said last month that it was deleting material from its YouTube channel that is older than 12 months to be in line with its policy of deleting content from its official website after a year.
Critics had slammed the station’s decision, saying it was against public interest and a waste of taxpayers’ money.
Netizens also accused RTHK of trying to ‘delete history’ by removing controversial programmes such as the highly popular Hong Kong Connection documentaries and the now-axed satirical show Headliner.