New tests, which are compulsory for all children starting primary school this term, could play a part in deciding how young children are grouped.
Charles Clarke, the schools minister, said he was sympathetic towards the idea of more setting and streaming in primary schools. He said that the tests' purpose was to tell teachers what children could do, not to provide a basis for setting, but added: "Teachers should use all the evidence, of which this assessment will be a relatively small part, if they are going to go down the road of setting.
"It would be a mistake for a teacher to rely entirely on these assessments in taking a decision about setting or streaming."
Research into the results of pilot tests show that girls' performance surpasses boys even at the age of four or five, suggesting that lower primary school sets may be dominated by boys.
Teachers and parents argued that it was dangerous to associate "baseline assessments" for five-year-olds with setting, which separates children into groups by ability for different subjects. Streaming, by contrast, separates groups of children for all subjects.
Mr Clarke urged parents not to coach children for the tests.
Assessments, which must be carried out in the first seven weeks of term, will include recognising and writing numbers one to 10, writing and spelling their own names correctly, recognising letters by shape and sound, and concentrating without supervision for 10 minutes.
Mr Clarke said coaching could be "counter-productive" because it is important that teachers and parents "understand directly, openly and honestly what a child's capabilities are".
However, the Government is sending out a million leaflets to parents explaining how they can help their child to do well at school by talking to them, counting with them, encouraging them to use new words and showing them how to write their names using capital and lower-case letters.
The tests have three purposes: to improve teachers' knowledge of their pupils; to measure pupils' progress and therefore schools' effectiveness; and to encourage more co-operation between parents and teachers.
For the first time, ministers argue, teachers will know how to help the slowest and stretch the brightest pupils.
Parents who were unhappy with the assessment results should discuss them with teachers, Mr Clarke said. "One of the most damaging aspects of the way children are taught in this country is that there is not enough understanding between parents, teachers and children."
Margaret Tulloch, chair of the Campaign for State Education, said: "If assessment is going to play even a small part in deciding what group children are going to be taught in, then of course parents are going to coach children. They won't want them turning up at age five and being put straight in the bottom set."
Doug McAvoy, general secretary of the National Union of Teachers, said baseline testing was designed to provide only a snapshot of children. "To overplay the role of baseline assessment in terms of setting is dangerous waters."
Most primary schools used informal grouping methods, with teachers responding from day to day to children's needs, he said. They would not want to start formal grouping of children in separate classrooms.
Ministers have said that assessing each pupil should take no longer than 20 minutes. Nigel de Gruchy, general secretary of the National Association of Schoolmasters/Union of Women Teachers, expressed concern about the workload. "I can only wonder what the other children in the class will be doing while one pupil is being individually observed and assessed."
John Coe, spokesman for the National Association of Primary Education, said setting could increase social division in schools.
"Middle-class parents will appreciate the importance of getting their children in the top set and so, of course, they will coach them."
Government sources said later that it was unlikely that many five-year- olds would be set by ability.Reuse content