Very able children and those with special educational needs are being sold short by the literacy hour, according to the latest study.
Eighty per cent of the 340 teachers surveyed by the Association of Teachers and Lecturers said the hour is not working for SEN pupils, and 60 per cent said the same for their most able children.
Meanwhile, three-quarters of the respondents said the paperwork was unmanageable, while 46 per cent said they spend four or more hours a week preparing for the hour.
The findings follow hard on the heels of two other reports from teaching unions.
One, carried out by the National Union of Teachers, showed that most of the 500 respondents were ambivalent about the hour's effectiveness, and more than half had altered it to better suit their pupils.
This survey, and a separate study by the National Association of Schoolmasters Union of Women Teachers, raised strong concerns about the extra workload and the quality of training for the literacy strategy.
A fifth of teachers said they had received no training, and nearly 60 per cent had been trained by classroom colleagues under the "cascade" system. One in three said the training was not adequate for them to implement the hour.
Nearly half those surveyed by the ATL said the literacy hour was not suitable for their pupils' age group - rising to 61 per cent of those teaching four to six-year-olds. And more than a third of teachers said it was not succeeding with mixed-ability groups.
Peter Smith, general secretary of the ATL, said: "What jumps off the pages of the research is the concern of those who teach children with SEN. The literacy hour must be made to work for those who need it most. There is an equal question about whether above-average children are being stretched enough.
"There are clear lessons to be learned and important warnings about the National Numeracy Strategy, to be introduced in September."
The literacy hour drew both positive and negative comments from teachers taking part in the survey.
One said: "Children like structure. Children have made huge progress." But another warned: "The poorest and youngest find 30 minutes of class teaching difficult to cope with."
The literacy strategist, People, page 16